I would shine a flashlight down the standpipe and see if water is in the trap.
Is there a floor drain in the room too?
First off, Iam totally embarassed to ask this question. I am a Texas master plumber and have been so for 30 yrs. I plumbed a new house around a year ago using Pvc sch 40 drain and vent lines. I plumbed the washer drain with 2"drain going directly into 3" drain some 5"away and 1 1/2" vent. The trap T's off the vertical vent close to the floor. We ran vent towards back of house about 20' making sure it had correct rise on it. Now when the homeowners
Run washer they get a sewer gas smell occasionally from washer drain. So I thought it must be vent, I cut vent going towards back of house and installed an Auto vent in attic. Which are considered legal in our area. This took care of problem for around 2 monthes, now They are getting it again. Any ideas would be greatly appreciated. Something I just thought of. This house happens to be last house on this branch of sewer main. I wonder if sewer main could be building up enough gas to affect washer drain since its the most water going down sewer at a time. I might try installing 4" running trap on sewer coming out of house?
NO shame in asking ! We all scratch our scarred up heads pretty often !
I've had a washing machine start to stink real bad before and my customer SWORE it was the stand pipe. It WAS the washer .
How about putting in a laundry tub and draining it there ? Or a check valve somewhere in that 2" line?