Drainage and Waste Systems
Certification Examination|||questions
and answers with rationales/graded
A+/2026 update/100% correct
/instant download
Exam Code: DWS-2026-CERT
Total Questions: 80
Passing Score: 75% (60 correct)
Time Allowed: 120 minutes
Instructions: Choose the single best answer for each question. Correct answers
are highlighted in bold. A rationale follows each question.
Section 1: Fixture Units & Drainage Load Calculation (Questions 1-12)
1. According to the 2024 Uniform Plumbing Code, what is the drainage fixture unit
(DFU) value for a public lavatory faucet?
A) 0.5 DFU
B) 1.0 DFU
C) 1.5 DFU
D) 2.0 DFU
Rationale: UPC Table 702.1 assigns 1.5 DFU to a public lavatory; private
lavatory is 1.0 DFU.
2. A 4-inch horizontal drainage pipe at 1/8 inch per foot slope has a maximum
DFU capacity of:
A) 180 DFU
B) 216 DFU
C) 360 DFU
D) 480 DFU
,*Rationale: UPC Table 703.2 – 4" at 1/8" slope = 216 DFU; at 1/4" slope = 360
DFU.*
3. What is the minimum slope for a 3-inch sanitary drainage pipe under IPC 2024?
A) 1/16" per foot
B) 1/8" per foot
C) 1/4" per foot
D) 1/2" per foot
*Rationale: IPC 704.1 – pipe size < 4" requires 1/8" min slope; 4" or larger may
use 1/16" where approved.*
4. A commercial kitchen sink with a garbage disposal is rated at:
A) 1 DFU
B) 2 DFU
C) 3 DFU
D) 4 DFU
*Rationale: UPC 702.2 – disposal + sink = 3 DFU; standard kitchen sink alone = 2
DFU.*
5. To convert from DFU to expected gallons per minute (GPM) flow, the
commonly used factor is:
A) 1 DFU = 7.5 GPM
B) 1 DFU = 10 GPM
C) 1 DFU = 15 GPM
D) 1 DFU = 20 GPM
*Rationale: Hunter’s curve approximations – 1 DFU ≈ 7.5 GPM peak, but design
flow uses 1 DFU = 15 GPM for peak surge.*
6. A total load of 500 DFU on a building drain requires a minimum pipe size of
(UPC):
A) 3 inches
B) 4 inches
C) 5 inches
D) 6 inches
*Rationale: UPC Table 703.2 – 4" max = 360 DFU; 5" max = 840 DFU; 500 DFU
exceeds 4" capacity.*
, 7. What is the DFU value for a bathtub (private) with an integrated shower head?
A) 1.0 DFU
B) 2.0 DFU
C) 2.5 DFU
D) 3.0 DFU
*Rationale: UPC Table 702.1 – bathtub = 2 DFU; shower stall = 2 DFU; combined
single fixture = max 2 DFU.*
8. A washing machine standpipe (2 inches) has a DFU value of:
A) 1.5 DFU
B) 2.0 DFU
C) 3.0 DFU
D) 4.0 DFU
*Rationale: UPC 702.1 – domestic clothes washer = 3 DFU. Commercial washers
vary but domestic is standard 3 DFU.*
9. Which fixture has the highest DFU value among standard residential fixtures?
A) Water closet (1.6 gpf)
B) Service sink with trap
C) Bidet
D) Residential kitchen sink
*Rationale: Service sink (mop sink) with trap = 3 DFU; WC = 3 DFU also, but
service sink has higher potential solids load per code.*
10. A 6-inch building sewer with 0.5% slope has a maximum DFU of (IPC 2024):
A) 1,200 DFU
B) 1,800 DFU
C) 2,400 DFU
D) 3,000 DFU
*Rationale: IPC Table 710.1(2) – 6" @ 0.5% slope = 2,400 DFU (horizontal).*
11. The “continuous flow” DFU adjustment for a pump discharging into a gravity
drain is:
A) No adjustment
B) Multiply DFU by 1.5
C) Add pump flow in GPM / 15
D) Subtract 25%
Certification Examination|||questions
and answers with rationales/graded
A+/2026 update/100% correct
/instant download
Exam Code: DWS-2026-CERT
Total Questions: 80
Passing Score: 75% (60 correct)
Time Allowed: 120 minutes
Instructions: Choose the single best answer for each question. Correct answers
are highlighted in bold. A rationale follows each question.
Section 1: Fixture Units & Drainage Load Calculation (Questions 1-12)
1. According to the 2024 Uniform Plumbing Code, what is the drainage fixture unit
(DFU) value for a public lavatory faucet?
A) 0.5 DFU
B) 1.0 DFU
C) 1.5 DFU
D) 2.0 DFU
Rationale: UPC Table 702.1 assigns 1.5 DFU to a public lavatory; private
lavatory is 1.0 DFU.
2. A 4-inch horizontal drainage pipe at 1/8 inch per foot slope has a maximum
DFU capacity of:
A) 180 DFU
B) 216 DFU
C) 360 DFU
D) 480 DFU
,*Rationale: UPC Table 703.2 – 4" at 1/8" slope = 216 DFU; at 1/4" slope = 360
DFU.*
3. What is the minimum slope for a 3-inch sanitary drainage pipe under IPC 2024?
A) 1/16" per foot
B) 1/8" per foot
C) 1/4" per foot
D) 1/2" per foot
*Rationale: IPC 704.1 – pipe size < 4" requires 1/8" min slope; 4" or larger may
use 1/16" where approved.*
4. A commercial kitchen sink with a garbage disposal is rated at:
A) 1 DFU
B) 2 DFU
C) 3 DFU
D) 4 DFU
*Rationale: UPC 702.2 – disposal + sink = 3 DFU; standard kitchen sink alone = 2
DFU.*
5. To convert from DFU to expected gallons per minute (GPM) flow, the
commonly used factor is:
A) 1 DFU = 7.5 GPM
B) 1 DFU = 10 GPM
C) 1 DFU = 15 GPM
D) 1 DFU = 20 GPM
*Rationale: Hunter’s curve approximations – 1 DFU ≈ 7.5 GPM peak, but design
flow uses 1 DFU = 15 GPM for peak surge.*
6. A total load of 500 DFU on a building drain requires a minimum pipe size of
(UPC):
A) 3 inches
B) 4 inches
C) 5 inches
D) 6 inches
*Rationale: UPC Table 703.2 – 4" max = 360 DFU; 5" max = 840 DFU; 500 DFU
exceeds 4" capacity.*
, 7. What is the DFU value for a bathtub (private) with an integrated shower head?
A) 1.0 DFU
B) 2.0 DFU
C) 2.5 DFU
D) 3.0 DFU
*Rationale: UPC Table 702.1 – bathtub = 2 DFU; shower stall = 2 DFU; combined
single fixture = max 2 DFU.*
8. A washing machine standpipe (2 inches) has a DFU value of:
A) 1.5 DFU
B) 2.0 DFU
C) 3.0 DFU
D) 4.0 DFU
*Rationale: UPC 702.1 – domestic clothes washer = 3 DFU. Commercial washers
vary but domestic is standard 3 DFU.*
9. Which fixture has the highest DFU value among standard residential fixtures?
A) Water closet (1.6 gpf)
B) Service sink with trap
C) Bidet
D) Residential kitchen sink
*Rationale: Service sink (mop sink) with trap = 3 DFU; WC = 3 DFU also, but
service sink has higher potential solids load per code.*
10. A 6-inch building sewer with 0.5% slope has a maximum DFU of (IPC 2024):
A) 1,200 DFU
B) 1,800 DFU
C) 2,400 DFU
D) 3,000 DFU
*Rationale: IPC Table 710.1(2) – 6" @ 0.5% slope = 2,400 DFU (horizontal).*
11. The “continuous flow” DFU adjustment for a pump discharging into a gravity
drain is:
A) No adjustment
B) Multiply DFU by 1.5
C) Add pump flow in GPM / 15
D) Subtract 25%
