How to Test a Drain Waste Vent System

Locate an easily accessible opening to the DWV system and install the test gauge. Some gauges can be inserted into a threaded clean-out, while others are attached to a pipe using a screwdriver and clamp.

Seal off all openings to the DWV system. Use pipe dope on all clean-out plugs and tighten clockwise. Seal other openings, such as trap arms and vent pipes, with test plugs, caps or inflatable balls. Insert test balls into the pipe and inflate with a compressor or pump, insert and screw plugs into a pipe, and install test caps on the end of a pipe using a clamp and screwdriver.

Attach the air compressor hose to the test gauge fitting. Fill the system with air until the test gauge reads 5 pounds per square inch.

Remove the hose from the test fitting and turn off the compressor. The drain, waste and vent system must maintain an internal pressure of 5 pounds per square inch without introduction of additional air for 15 minutes to pass a plumbing inspection.

Check for leaks in the plumbing system or around the test fittings if the pressure drops below 5 pounds per square inch. Consult with a plumbing professional if you can't find the leak.

Remove the test gauge and test fittings after a successful test and plumbing inspection, including vent pipe caps on the roof. These can be easy to forget about but must be removed because your DWV system will not work properly if it does not get the proper air flow.