Plumber exam: Drainage and venting

Key points

• A trap holds a water seal to block sewer gas.
• Vents let air in so flowing water does not siphon trap seals.
• Small horizontal drains usually slope about 2% (1/4 in per foot).
• Fixture units add up to size drains and vents.
• Cleanouts are needed at changes of direction and at set distances.

Study tip

Check your provincial plumbing code for exact sizing tables. Questions follow the national code.

Try these

1. The main job of a vent is to:

   1. Carry waste
   2. Protect trap seals
   3. Raise water pressure
   4. Hold a cleanout
   Show answer

   B. Protect trap seals Venting stops siphonage.

2. A typical slope for a small horizontal drain is:

   1. 0.5%
   2. 1%
   3. 2%
   4. 5%
   Show answer

   C. 2% About 1/4 in per foot.

3. Drain sizing uses:

   1. GPM only
   2. Fixture units
   3. Pipe colour
   4. Trap depth
   Show answer

   B. Fixture units Fixture units add up loads.

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