UTILITIES | Plumbing Systems | 20 Questions (MODERATE-CHALLENGING)

PLUMBING SYSTEMS

(20 Questions, Difficulty Level: MODERATE to CHALLENGING)
by Raison John J. Bassig

For Q#1 to Q#3:
Given the installation of a sanitary waste branch as shown below,

Q#1: What is the maximum distance of the length "A" shown in the above illustration?
  a. 30"       b. 120"       c. 42"       d. 72"

Q#2: What must be the minimum distance of the length "A" shown in the above illustration?
  a. 12"       b. 6"         c. 3"        d. No prescribed minimum distance

Q#3: What is the maximum distance of the height "B" shown in the above illustration?
  a. 40cm      b. 60cm       c. 75cm     d. 100cm

According to the 1999 Revised National Plumbing Code of the Philippines (RNPCP) and the 1997 Uniform Plumbing Code (UPC) where the RNPCP was based on,

"Each fixture trap shall have a protecting vent so located that the developed length of the trap arm from the trap weir to the inner edge of the vent shall be within the distance given in Table 10-1, but in no case less than two times the diameter of the trap arm."
(Sec. 1002.2 of the 1999 RNPCP and Sec. 1002.2 of the 1997 UPC)

(Horizontal Distance of Trap Arms, Table 10-1 of the 1999 RNPCP and the 1997 UPC)

*Note that Developed Length is defined in the Code as "the length of a pipe along its centerline and fittings."

In my illustration above, since the size of the trap arm is 3" (or ~76mm) diameter, then, based on Table 10-1 of the Code, the maximum horizontal distance of the trap arms (from the trap weir to the inner edge of the 2" vent), should be 1.83m. Converting [1.83m] to the units given in the choices,

Maximum Horizontal Distance = 1.83m = 1.83m x (1000mm/1mm) x (1"/25.4mm) = ~72"

As to the minimum horizontal distance, according to the provisions of the Code, must be twice the diameter of the trap arm. Since the given size of the trap arm is 3", then,

Minimum Horizontal Distance = 2 x [ Diameter of Trap Arm ] = 2 x 3" = 6"

As to the height of the drain fixture to the trap (i.e., the length of the tailpiece), the Code specifically states that,

"The vertical distance between a fixture outlet and the trap weir shall be as short as practicable, but in no case shall the tailpiece from any fixture exceed 0.6 meter in length."
(Sec. 1001.4 of the 1999 RNPCP)

"The vertical distance between a fixture outlet and the trap weir shall be as short as practicable, but in no case shall the tailpiece from any fixture exceed twenty-four (24) inches (610mm) in length."
(Sec. 1001.4 of the 1997 UPC)

Therefore:

The correct answer for Q#1 (maximum length of trap arm) is d. 72" (or 1.83m or 6' or 1829mm).

The correct answer for Q#2 (minimum length of trap arm) is b. 6" (or 2x diameter of trap arm).

The correct answer for Q#3 (maximum length of tailpiece) is b. 60cm (or 0.6m or 24" or 610mm).

For Q#4 to Q#7:

In a 23-storey building (without basements) and having typical toilets in each and every floor, a continuous 4"Ф Soil Stack is provided for the purpose of serving all the typical horizontal soil branch lines from the Ground Floor (GF) up to the 23rd Floor (23F) as shown in the illustration.

Near the said soil stack, another continuous stack, a 3"Ф Vent Stack, is also installed with the intention of providing auxiliary ventilation (using yoke-relief vents) between the two stacks.

Q#4: At which point along the Soil Stack must a yoke vent be provided?

1. Above the floor and the highest overflow level of a fixture served by the drain branch
2. Below the floor and immediately above the drain branch connection to the soil stack
3. Below the floor and immediately below the drain branch connection to the soil stack
4. Yoke vent must be connected to the drain branch itself and not at the soil stack

Q#5: At which point on the Vent Stack shall the yoke be connected to act as a relief vent?

1. Below the floor and immediately above the drainage branch connection to the soil stack
2. At any point along the vent stack
3. Below the floor and immediately below the drainage branch connection to the soil stack
4. Above the floor and the highest overflow level of a fixture served by the drain branch

Q#6: What is the minimum pipe size for the yoke-relief vents in the illustrated scenario?
  a. 4"       b. 2"       c. 3"       d. 1-1/2"

Q#7: Based on the illustration, at which specific floors served by its corresponding soil branches shall these yoke-relief vents be located, at the very least, to conform with the Code?

1. At 3F, at 8F, at 13F, at 18F, and at 23F
2. At GF, at 3F, at 6F, at 9F, at 12F, at 15F, at 18F, at 21F, and at 23F
3. At GF, at either 11F or 12F (midpoint of the topmost and bottom floors), and at 23F
4. At 5F, at 10F, at 15F, at 20F, and at 23F

According to the 1999 Revised National Plumbing Code of the Philippines (RNPCP) and the 1997 Uniform Plumbing Code (UPC) where the RNPCP was based on,

"Each soil or waste stack which extends ten (10) or more stories above the building drain shall be served by a parallel vent stack which shall extend undiminished in size from its upper terminal at the roof and connect to the soil or waste stack at ground level and at every fifth floor levels with a "yoke vent" at a point below the horizontal soil or waste branch connection to the stack and at the nearby vent stack above the same floor to provide a relief vent. The size of yoke vent shall be not less in diameter than either the soil stack or the vent stack, whichever is smaller."
(Sec. 907.1 of the 1999 RNPCP)

"Each drainage stack which extends ten (10) or more stories above the building drain or other horizontal drain, shall be served by a parallel vent stack which shall extend undiminished in size from its upper terminal and connect to the drainage stack at or immediately below the lowest fixture drain. Each such vent stack shall also be connected to the drainage stack at each fifth floor, counting down from the uppermost fixture drain by means of a yoke vent, the size of which shall be not less in diameter than either the drainage or the vent stack, whichever is smaller." (Sec. 907.1 of the 1997 UPC)

Therefore:

The correct answer for Q#4 is c. Below the floor and immediately below the drain branch connection to the soil stack.

The correct answer for Q#5 is d. Above the floor and the highest overflow level of a fixture served by the drain branch.

The correct answer for Q#6 is c. 3".

The correct answer for Q#7 is a. At 3F, at 8F, at 13F, at 18F, and at 23F.

For Q#8 to Q#9:
In the installation of urinals as shown in the photo below,

(Photo courtesy of Ron Knox 2001 via Flickr, modified with annotations)

Q#8: What is the minimum clearance of distance "A" as shown in the above photo?
  a. 375mm       b. 300mm     c. 250mm     d. 450mm

Q#9: What is the minimum clearance of distance "B" as shown in the above photo?
  a. 0.75m       b. 0.9m       c. 0.5m       d. None of the given choices

According to the 1999 Revised National Plumbing Code of the Philippines (RNPCP) and the 1997 Uniform Plumbing Code (UPC) where the RNPCP was based on,

"Setting - fixtures shall be set level and in proper alignment with reference to adjacent walls. No water closet or bidet shall be set closer than 0.375 meter from its center to any side wall or obstruction nor closer than 0.75 meter center to center to any similar fixture. No urinal shall be set closer than 0.3 meter from its center to any sidewall or partition nor closer than 0.6 meter center to center."
(Sec. 407.5 of the RNPCP)

Therefore:

The correct answer for Q#8 (minimum distance from urinal centerline to partition or sidewall) is b. 300mm.

The correct answer for Q#9 (minimum distance from center-to-center of urinals) is d. None of the given choices (the clearance should be 0.6m).

For Q#10 to Q#15:
In locating components for a Sewage Disposal System on a site given in the illustration,

Q#10: How far at least must the Septic Tank be from a tree, at distance "B" as shown above?
  a. 3 meters (10’)   b. 2.4 meters (8’)   c. 1.5 meters (5’)   d. 0.6 meter (2’)

Q#11: Minimum distance "D" between Disposal Field and adjoining private property line:
  a. 3 meters (10’)   b. 2.4 meters (8’)   c. 1.5 meters (5’)   d. No minimum distance

Q#12: How far at least must the Disposal Field be from a tree, at distance "F" as shown?
  a. 0.6 meter (2’)    b. 2.4 meters (8’)   c. 1.5 meters (5’)   d. No minimum distance

Q#13: Minimum clear distance of Disposal Field from the stream, at distance "G" as shown:
  a. 30.5 meters    b. 45.7 meters    c. 15.2 meters    d. No minimum distance

Q#14: How far at the minimum must the Septic Tank be from the well, at distance "J"?
  a. 100 feet       b. 150 feet       c. 10 feet       d. 50 feet

Q#15: Minimum distance between Disposal Field and structure, at distance "K" as shown?
  a. 3 meters (10’)   b. 2.4 meters (8’)   c. 150 feet      d. 100 feet

According to the 1999 Revised National Plumbing Code of the Philippines (RNPCP) and the 1997 Uniform Plumbing Code (UPC) where the RNPCP was based on,

(Location of Sewage Disposal System, Table B-1 of the 1999 RNPCP and Table K-1 of the 1997 UPC)

Therefore:

The correct answer for Q#10 (clearance of Septic Tank from Trees) is a. 3 meters (10’).

The correct answer for Q#11 (clearance of Disposal Field from Adjoining Property Line) is c. 1.5 meters (5’).

The correct answer for Q#12 (clearance of Disposal Field from Trees) is d. No minimum distance.

The correct answer for Q#13 (clearance of Disposal Field from Streams) is c. 15.2 meters (or 50 feet).

The correct answer for Q#14 (clearance of Septic Tank from Water Supply Wells) is d. 50 feet (or 15.2m).

The correct answer for Q#15 (clearance of Disposal Field from Buildings/Structures) is b. 2.4 meters (8’).

Q#16: The "scum" in a sewage disposal system or septic tank:

1. Solid organic matter, denser than water, that settles at the bottom of the tank
2. Liquid content of the sewage
3. Lighter organic materials that rise to the surface of the water
4. An unwanted person on the face of the earth

The following definitions pertain to choices a, b, and c, respectively:

Sludge:
"Sediment that settles out of sewage, forming a semi-solid mass on the bottom of a septic tank."
(Page 201, A Visual Dictionary of Architecture by Francis D.K. Ching)

Effluent:
"Liquid sewage that has been treated in a septic tank or a sewage treatment plant."
(Page 201, A Visual Dictionary of Architecture by Francis D.K. Ching)

Scum:
"A layer of sewage matter that rises to the surface of the sewage in a septic tank."
(Page 201, A Visual Dictionary of Architecture by Francis D.K. Ching)

Therefore, the correct answer is c. Lighter organic materials that rise to the surface of the water.

Q#17: Which of the following conditions is acceptable and conforms with the Code?

1. When determining the size of the septic tank based on Code guidelines, those water closets that are for private use shall be computed with a drainage fixture unit (DFU) of 4.
2. A vent branch of 76mmФ in size can be installed up to 84 meters in total length.
3. Using a 76mmФ x 102mmФ double sanitary tee for a horizontal drain branch connecting to a vertical stack is permitted.
4. Fixtures connected to a grease trap must not be individually trapped.
5. All of the above (i.e., all the choices given conform with the provisions in the Code).

Let's look at each of the given choices and check its corresponding provisions in the 1999 Revised National Plumbing Code of the Philippines (RNPCP) and the 1997 Uniform Plumbing Code (UPC) where the RNPCP was based on,

Choice a., the Drainage Fixture Unit of a private water closet, can be seen in the Code,

Despite the Water Closets in private installations have a DFU = 4, the Code specifically states that when calculating the Septic Tank capacity, such Water Closets must be computed at a DFU = 6.

As such, choice a. is in violation of the Code.

Choice b., the maximum length of a vent branch, is provided for in the Code,

As you can see, the maximum pipe length are limited for vertical drainage pipes (soil or waste stacks), vertical vent pipes (vent stacks), and horizontal vent pipes (vent branches). There is no limit provided by the Code on the length of pipe if it is used for horizontal drainage (soil or waste branches).

Since the given vent branch (i.e., horizontal vent) is only 76mmФ (~3"Ф) in size, the maximum length according to the Code, is only up to 65 meteres. So, choice b., at 84 meters, will violate the Code.

Choice c., the use of a double sanitary tee for horizontal-to-vertical connection, is provided for in the Code,

"Horizontal drainage branch lines, connecting with a vertical stack, shall enter through 45 or 60 degree wye branches, combination wye and 1/8 bend branches, sanitary tee or sanitary tapped tee branches or other approved fittings of equivalent sweep. x x x Double sanitary tees may be used when the barrel of the fitting is at least two (2) pipe sizes larger than the largest inlet, (pipe sizes recognized for this purpose are 51, 64, 76, 89, 102, 114, 127 & 152mm diameters, etc.)."
(Sec. 705.2 of the 1999 RNPCP and in consonance with Sec. 706.2 of the 1997 UPC)

The size of the double sanitary tee is given as 76mmФ x 102mmФ (i.e., 76mm inlet and 102mm barrel), with the inlet having a difference of two pipe sizes compared to its barrel according to the Code provision (i.e., one pipe size above 76mm is 89mm, two pipe sizes above 76mm is 102mm).

Since such fitting will be used to connect a horizontal branch to a vertical stack, then, choice c. conforms with the Code.

Choice d., fixtures discharging into a grease trap, is governed by the Code as,

"Each fixture discharging into a grease trap shall be individually trapped and vented in an approved manner. x x x"
(Sec. 1011.5 of the 1999 RNPCP and Sec. 1014.5 of the 1997 UPC)

As the Code states, despite the fixture already connected to a grease trap, such fixture must still be provided with an individual trap and protected by a vent.

Thus, choice d. will not conform with the Code.

Therefore, the correct answer is c. Using 76mmФ x 102mmФ double sanitary tee for a horizontal drain branch connecting to a vertical stack.

Q#18: If a certain fixture is assigned a Drainage Fixture Unit (DFU) of 2, what is its equivalent discharge capacity considering intermittent flow?

1. 1.95 L/sec to 3.15 L/sec
2. 8 gpm to 15 gpm
3. 1.00 L/sec to 1.89 L/sec
4. Approximately 28.2 L/min
5. 16 to 30 gpm

According to the 1999 Revised National Plumbing Code of the Philippines (RNPCP) and the 1997 Uniform Plumbing Code (UPC) where the RNPCP was based on,

(Discharge Capacity, Table 7-3 of the 1999 RNPCP and Table 7-4 of the 1997 UPC)

Therefore, the correct answer is b. 8 gpm to 15 gpm.

Q#19: A vent serving two or more traps and extending from in front of the last fixture connection of a horizontal branch to the stack vent.

1. Circuit Vent
2. Common Vent
3. Loop Vent
4. Back Vent
5. Relief Vent

According to the 1999 Revised National Plumbing Code of the Philippines (RNPCP), under definition of terms,

"CIRCUIT VENT - a group vent pipe which starts in front of the extreme fixture connection on a horizontal branch and connects to the vent stack. See loop vent, also."
(Sec. 204.8 of the 1999 RNPCP)

"COMMON VENT (see unit vent). UNIT VENT - an arrangement of venting so installed that one vent pipe will serve two (2) traps."
(Sec. 204.11 and Sec. 222.2 of the 1999 RNPCP)

"LOOP VENT - a vertical vent connection on a horizontal soil or waste pipe branch at a point downstream of the last fixture connection and turning to a horizontal line above the highest overflow level of the highest fixture connected thereat; the terminus connected to the stack vent in the case of loop venting or to the vent stack nearby in the case of circuit venting."
(Sec. 213.12 of the 1999 RNPCP)

"BACKVENT PIPE - the part of a vent line, which connects directly with an individual trap underneath or behind the fixture and extends to the branch or main vent pipe at any point higher than the fixture or fixture traps it serves. This is sometimes called an individual vent. See Revent pipe."
(Sec. 203.7 of the 1999 RNPCP)

"RELIEF VENT - a vertical vent line, the primary function of which is to provide additional circulation of air between the drainage and vent systems or to act as an auxiliary vent on a specially designed system such as a "yoke vent" connection between the soil and vent stacks."
(Sec. 219.3 of the 1999 RNPCP)

In other words, a circuit vent connects to the VENT STACK, while a loop vent connects to the STACK VENT.

Below is my illustration of some of the vent systems mentioned (take special note of the difference between the circuit vent and the loop vent),

Therefore, the correct answer is c. Loop Vent.

Q#20: Which of the following is prohibited based on provisions of the Code?

1. Drinking fountains may be installed with indirect wastes.
2. No additional cleanouts are required for horizontal lines with an aggregate offset angle of direction less than 135°.
3. Indirect waste pipes measuring 3.0 meters in length must be provided with a trap but need not be vented.
4. If the horizontal drainage line serving a sink is only 1000mm in length, a cleanout on such line must still be provided.
5. None (all the choices given above conform to the Code).

Let's look at each of the given choices and check its corresponding provisions in the 1999 Revised National Plumbing Code of the Philippines (RNPCP) and the 1997 Uniform Plumbing Code (UPC) where the RNPCP was based on,

Choice a. is a direct (verbatim) reference to the actual provision found in the Code,

"Drinking fountains may be installed with indirect wastes."
(Sec. 809 of the 1999 RNPCP and the 1997 UPC)

This means that drinking fountains installed with indirect wastes are allowed in the Code.

Choice b. gives us a horizontal drain line with a change in direction that is less than 135° and not provided with an additional cleanout. In the Code,.

"An additional cleanout shall be provided on a horizontal line with an aggregate offset angle of direction exceeding one hundred and thirty-five (135) degress."
(Sec. 706.2 of the 1999 RNPCP and in consonance with Sec. 707.5 of the 1997 UPC)

Since the angle did not exceed 135°, then, no additional cleanout is required. This means that choice b. (i.e., no additional cleanouts if less than 135° change in direction) also conforms to the Code.

Choice c., given a 3m-long indirect waste pipe with an unvented trap, is within the Code provision as traps are required for such indirect waste pipes between 1.5m and 4.6m long, with the trap permitted to be unvented.

"Indirect waste pipes exceeding 1.5 meters but less than 4.6 meters length shall be directly trapped, but such traps need not be vented."
(Sec. 803 of the 1999 RNPCP and in consonance with Sec. 803 of the 1997 UPC)

Since the given pipe length falls between 1.5m and 4.6m, a trap is required but does not need to be venter. This means that choice c. also conforms with the Code.

Choice d., with a required cleanout on a 1m-long horizontal drain line serving a sink, is also Code-conforming since cleanouts may only be omitted for horizontal drain lines less than 1.5m in length if such drain line is not serving sinks or urinals.

"Cleanouts may be omitted on a horizontal drain line less than 1.5 meter in length unless such line is serving sinks or urinals."
(Sec. 706.1.1 of the 1999 RNPCP and in consonance with Sec. 707.4.1 of the 1997 UPC)

Despite the given length of the horizontal drain is only 1 meter (less than 1.5 meter), it will still require a cleanout as the given drain line specifically serves a sink. So, such installation also conforms with the Code.

Therefore, the correct answer is e. None (all the choices given above conform to the Code).