Basement Floor Drain Problem

The water level in my basement floor drain keeps dropping, thereby allowing sewer gas up the drain. The trap is not drying out because it happens within a day. The water level drops about .5 inches, just enough to let some gas up.

The behvior is inconsistent so I am not sure if it is a crack in the trap. The water level usually drops when our overhead ejector pump is used quite a bit throughout the day. The overhead plumbing connects to the main stack, which is about 6 feet from the floor drain.

Any ideas? Could the ejector pump cause the water in the trap to be siphoned out?

All traps need to be vented, otherwise they are subject to siphoning...I'd guess if it has a trap, it is not vented. 1/2" drop doesn't seem like enough to open the trap to allow gas. You sure it isn't just uncovering some sludge? Try some bleach and scrub the top of the drain and see if it helps any.

Still need help

I assumed that the main stack acts as the vent for the floor drain. I scrubbed the drain pipe with bleach and filled up the trap again. However, the water level in the trap keeps dropping. After further inspection it is dropping 1-2 inches. Sewer gas enters once the level decreases.

So I fill the trap with a bucket of water and it's fine for awhile. I am still have difficulties isolating when the level drops, but it does consistently occur after the ejector pit runs for a couple loads of laundry. Also, we do have a catch basin and I suspect that it is tied into the sewer upsteam from the floor drain.

My initial thoughts are siphoning or a crack in the drain pipe. Any suggestions would be much appreciated.

Probably isn't vented properly.

hi jpj,
i think it may very well be vented adequately, but no one will ever know until you tell us the details. E.g. 2" drain, X feet from stack, no other plumbing in basement, etc. Was it working perfectly for 50 years before this suddenly changed, etc.

Your sense of analysis is good. Add water and the seal is back. Then, figuring out why water leaves the trap is a dilemma. You have listed two possible reasons. One, trap now cracked. Two, trap water being drawn out... and this could happen if another vent, perhaps quite far away, is now blocked, because then venting in general is not up to par, and that might cause the trap's water to be pulled out by the ejector pump downstream.

Seems you have not yet been able to find a cause and effect. Can you stop the ejector pump completely for the time it takes to see if the trap empties? Secondly, try and see if sealing off the floor drain (plastic bag), changes anything else in the house plumbing (venting and draining) e.g. like a toilet filling to a higher level before the flush happens.

David