How to Finish a Basement Bathroom – Part 10

How to Finish a Basement Bathroom: Sewage basin plumbing connections to the roof vent pipe. This project is continued from How to Finish a Basement Bathroom – Part 9. See the series introduction for the project index.

The purpose of the sewage basin vent pipe is to equalize the air pressure as the water level changes in the basin. Air moves in and out the vent pipe as follows:

  • Air outflow: As waste water fills the sewage basin – for example when flushing the toilet, running the sink faucet or shower – air in the basin exhausts through the vent pipe to the outdoor roof vent to prevent pressurizing the sewage basin.
  • Air inflow: When the sewage basin is full the pump float switch is triggered, the sewage pump switches On and air fills the sewage basin to replace the water volume pumped out.

If the sewage basin is not correctly vented then bad things can happen including sewer gas odors, slow drains and water backing out of the bathroom drains.

Fortunately the roof vent pipe to the outdoors was roughed-in when the home was built so I only had to make the interior vent pipe connections to the basement sewage basin. See the Venting for Plumbing Systems presentation by the Plumbing and Mechanical Association (PMA) of Georgia for excellent introduction to Drain and Waste Vent systems.

The sewage basin 2 inch PVC vent pipe was easy to install:

  • Measure, cut and dry-connect the PVC pipe sections to ensure everything fit properly.
  • Take apart the pipe and fittings.
  • Glue and permanently install the PVC vent pipe.

Basement Bathroom Sewage Basin Vent Pipe Plumbing

Blue lines in the next set of photos highlight the basement bathroom air vent pipe plumbing from the sewage basin to the outdoor roof vent. The PVC vent pipe extends about 3 inches below the metal cover of the sewage basin (which is well above the pump float switch high water level; the vent pipe must never be in contact with the waste water) and sealed by a rubber grommet:

Basement Bathroom Sewage Basin Vent Pipe Plumbing

Basement Bathroom Sewage Basin Vent Pipe Plumbing

Tip: Lubricate the rubber grommet with a liquid soap to insert the PVC pipe.

A threaded 2 inch Schedule 40 PVC slip union (slip x slip or S x S union) is installed in the sewage basin vent pipe about six feet above the concrete floor. The slip union provides clearance to disconnect the lower portion of the vent pipe to remove the sewage basin metal lid; I didn’t want the vent pipe knocking me in the head when working on the sewage ejector pump. Horizontal sections of the vent pipe are supported by metal hanger straps fastened to the floor joists:

Basement Bathroom Sewage Basin Vent Pipe to the Roof Vent

Basement Bathroom Sewage Basin Vent Pipe to the Roof Vent

Detail of the bracing block and metal support strap extending from the wall. The air vent pipe is right side of the photo:

Basement Bathroom Plumbing: PVC Pipe Support Straps and Blocks

Basement Bathroom Plumbing: PVC Pipe Support Straps and Blocks

A different angle of the 2 inch PVC vent pipe (right) entering the metal cover of the sewage basin:

Basement Bathroom Plumbing: Sewage Basin PVC Waste and Vent Pipes

Basement Bathroom Plumbing: Sewage Basin PVC Waste and Vent Pipes

The sewage basin high water alarm is installed in How to Finish a Basement Bathroom – Part 11.

Regards,

Bob Jackson

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