So we moved into this house, and it has a lift pump for JUST the washer standpipe and water softener, and it pumps into the existing plumbing somewhere then out to the city sewer.

The plumbing setup

I’ve never had or lived in a house with this setup, and I’m still learning how it works.

Nevermind how close the NON-GFCI outlet is to the standpipe, I’m not using it

It seems that the standpipe enters the crock through the pipe on the left, which is also vented, and connects to the vent pipe coming out the top of the crock on the left.

Vent routing, it crosses to the left then up into oblivion... hopefully the roof

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The right is the grey water exit from the pump, with a one-way valve that empties into a pipe in the rafters, hidden by insulation and drop ceiling.

Professionally cord wrapped water outlet that probably leads to the rest of the plumbing... somewhere

I assume it empties into the iron waste pipes near the front of the house, covered by wall, but the clean out is accessible through this handy ‘vent’.

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Hi, hopefully sealed non-leaking Iron Giant

So, the issue.... when we run the first load of laundry after not using it for a week, we get a STRONG SMELL OF METHANE/SEWER in the basement.

It is hard to trace, because it hasn’t happened EVERY time we run the washer after a week, or the water softener cycles. By then the whole basement smells, and after being down there for ~30 seconds, I get used to the smell and can’t find its source. It happened the day after we moved in and I ran a load of laundry, and it happened last night. Last week - no steenk.

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In my searching around online I think the cause is sewer gasses coming from the crock cover, which isn’t solid, and appears to have a crack in it.

Not sure if pressboard.... plastic.... gonna caulk the shit outta it

I read that ‘caulking the shit’ out of the cover might help, and I’m going to start there tonight, but I was wondering if the way the vent is run is also an issue. Should it be run off the standpipe the way it is (second image) or just off the crock?

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Is it possible the gas is escaping ELSEWHERE in the piping, but is only affected with the laundry standpipe/lift pump?

I’m gonna start pulling down the ceiling if the caulk doesn’t help, but not being a plumbing expert I was wondering if anyone else sees something I can’t.