Hello,

We have a situation in regards to our sewer drain that the washer drains into. We have been in this house for 5 years and we never had a sewer odor from the washer standpipe. We purchased a new washer ~1 year ago and we notice sewer gas coming from the standpipe after the washer runs a load. We either have to pour water down or remove the washer drain line and plug it up with a old rag to prevent the odor from coming out. The washer is on our main level and there is a crawl space below. I have went in the crawl space and verifified that there is a P trap on the line. I have went on the roof and snaked the vent and there is no blockage. I even ran water from the garden house down the top of the vent while in the crawl space and can hear the water running in the lines. It is almost as if the trap is not holding water, but there is no leaking from the line. The trap is about 40 inches from the top of the standpipe. The washer discharge line only extends into the standpipe about 6 inches, so there is at least another 34 inches of straight pipe until it reaches the trap. The drain line doesn't back-up or overflow. I am starting to think that the washer discharges much more water quicker than the old washer and it is somehow creating a siphon on the trap? Not sure if that is common or not and if so, how to correct it.

Any advise or insight is greatly appreciated.

Thank You,
Nick

 

What is the size of your washer drain line? Current code requres 2" because of the high flow rate of some machines.

Since you've been underneath and looked at the trap. Compare it and the vent connect ion to some examples of proper drain plumbing. If the piping is not run correctly it can siphon the water out of the trap.

 

The drain line is 1.5", so I am guessing that the permanent fix would be to replace the 1.5" drain line and trap with a 2" inch line.

Thanks for the input.

 

While the larger pipe will probably help, my guess is that there's no vent on the line past the trap (within 6-8'). Newer washers are higher efficiency and dump water out more quickly, which might be causing the trap to suck dry. It's like flushing a toilet, if you flush slowly, the trap doesn't empty. If you flush quickly, the trap and all the water (and waste) drains out.

 

The vent is about 12 feet away from the trap, but it is not downstream of the line, it is upstream. If that makes sense. So, from my limited understanding, it sounds like the line needs to be vented closer to the trap and downstream (past) the trap?

Thanks

 

Yes.
Though I'm not quite understanding what you mean by the trap being upstream from the laundry standpipe? Can you sketch out how the piping is actually set up?

 

This is a very rough sketch. The Laundry drain is ~12 feet downstream of flow from the vent.