Q: My client has a sewer ejection tank in his basement for a laundry and a half-bath. When the washer drains and the tank pumps out, the liquid overwhelms the vent's ability to supply enough makeup air, causing a "pull" on nearby traps (mainly the first-floor toilet). What is the proper way to vent this system, and can I add venting to remedy this situation?
A: Mike Casey, a licensed plumbing contractor and ICC Certified Combination Inspector in San Diego responds: Clothes washers pump out a lot of water quickly, which can put a load on the sewage ejector pump. But that shouldn't affect the traps connected to the sewage ejector tank if it's properly vented.
The ejector tank should be vented by a connection to the top cover that's at least 1 1/2 inches in diameter, although 2-inch vent pipe is common in this application. The tank vent should be a dry vent that either terminates at the exterior of the house or connects to another dry vent that terminates at the exterior. In addition to the sewage ejector tank being vented, each of the plumbing fixtures connected to the tank must be properly vented, and all the plumbing fixtures in the remainder of the house must be correctly vented as well.
In your situation, I suspect that there is inadequate or even a total lack of venting at the ejector tank and possibly at the first-floor toilet as well. Determining the scope of the repair will require some investigation to ascertain the existence and adequacy of venting at all fixtures. I would also be sure to check the vent terminals (stack pipes) on the roof to establish that they are free from any obstructions.
If your jurisdiction allows it, you may be able to add an air admittance valve (AAV) to any plumbing fixtures that need venting. When properly installed, AAVs can be an inexpensive way to add venting in many places. However, be aware that an AAV cannot be used for venting a sewage ejector tank.
The principles and requirements for plumbing vents can be very technical, so I'd recommend having a licensed plumber inspect and evaluate the system to determine the best and most cost-effective method to correct your specific problem.