Laundry sewer smell & no trap question

Hi everyone. Quick and hopefully easy question.

We have a first floor laundry room and get occassional stankiness that I believe is coming from the washer. The washer drain pipe runs down through the wall into a crawlspace and then makes an 8ft. horizontal run where it joins a primary waste pipe (another 15-20 ft. horizontal run) that leads eventually out to the septic field. Both the horzontal run of the washer drain pipe and the primary waste pipe look to have a slight downward slope which I guess would be expected.

The problem (I think) is that there is NO TRAP on the washer drain pipe.

My question is three parts:

Should there be a trap?

If so, can I install it mid-way along the horizontal run of the washer drain pipe rather than at the bend where the vertical goes horizontal? (there is very limited working space in the crawlspace).

If the answer is yes, are there any guidlines on the dimensions of the trap - i.e., do I have to worry about staying above the level at which the main drain pipe goes out to the septic or any such thing?

Thanks very much in advance for any help!

As I understand it, it should have both a trap AND a vent. With it open to your septic system, it can leak noxious fumes into the house. WIthout a vent, it would siphon out the trap and still let those fumes into the house. My unprofessional experience.

Vent

I believe it is vented (have to look when I get home) to the main DMV stack before the primary drain line goes out to the septic, but I imagine that without the trap in place, it's allowing some (but not all) fumes to travel back up the drain pipe to the washer. It actually is probably acting as a mini-vent, unfortunately on the inside of the house, without the trap...?

The vent should be just above the floor level, not in the crawlspace.

In order to function as a vent for the washer, it must be within the prescribed distance of the trap. I don't know that distance, but I'd guess it is no more than about 5' (and closer is probably better). One of the pros will know off the top of their head.

My bad

I explained it incorrectly. There is a 1 1/2" vertical copper pipe that runs up about 3/4 of the washer height behind the washer. The washer drain hose fits into this pipe. There is some air space around where it goes into the pipe, which is where I think the stank is coming from.

The pipe then travels down between the wall studs, through the floor, where it goes into a 90 degree elbow to make it run horizontally. This is in the crawlspace. It then catches the drain waste pipe coming from the toilet (located in the same room) about 5-6 feet away by means of a "Y" fitting. Then that drain waste pipe is vented through the roof, and the horizontal run continues to to septic junction about 20 feet away. So I think it is vented properly now that I've had another look at it.

My question is about whether I need a trap, and whether I can install it along the 5-6 foot horizontal run before the "Y" fitting and the vent. If so, are there any gravity-related considerations as to how deep the trap would need to be? I plan on cutting out a section of the 1 1/2" copper washer drain pipe along the horizontal, getting a couple of copper-to-PVC neoprene fittings, and making the trap out of PVC.

Thanks again - really appreciate the help!

The trap should be right at the base of the standpipe, before the pipe drops into the basement. Be sure to install it with at least a 4" trap arm length so it is not an "S" trap. Also, there should be a vent connection, usually within 8 feet if this is a 2" pipe.


It should be a 2" pipe, but I reread your post and see that it is 1½, so the vent should be within 5 or 6 feet.

OK - got it - thanks again guys. Great forum and truly appreciate the help!

my 2 cents

as it starts ,so it goes ! if the installer didn't know about traps, they didn't know about vents. from what you say , you gave us no reason to believe this run is vented. PLEASE have a plumber help you, it,s your health! change to 2" 1 1/2 is to small