Settle a dispute for me: Is the drain for a washing machine supposed to have a trap?

Yes,

See the images below and you will know, Thanks.

John

Absolutely. Every plumbing fixture in your house HAS to be trapped. No way around it. Trap creates seal keeping sewer gas from escaping into your house. Absence of trap creates health hazard for house occupants.

Usually, you cannot see the washing machine trap because it is built into the framing of the wall and covered with drywall.

Thanks for the reply. I thought that was the case.

Here is the basic rule: if it drains it needs a trap, if it has a trap it needs to be vented.

Well, let me just ask the next logical question in my education on this subject. How far away can the vent be from the trap and still work?

I noticed a comment from Speedball recently about the importance of the vent in having a good, swift water flow down the waste pipe in order to keep it clean. "Self-scouring", I think was his term. That was interesting.

It depends what Code you fall under the allowable distances of vent from trap vary. I work under UPC. So, in your case, you would need 2" drain for W/M and you can go up to 48" before you have to have vent.

1 1/2 " = 3 ft 6 in.
2" = 4 ft.
3" = 5 ft.

let me just ask the next logical question in my education on this subject. How far away can the vent be from the trap and still work?
As Milo sez, It all dependa upon what code you fall under. Mine, (SPC) will let you go 5' on 1 1/2" and 6'on 2". Go figure! Tom

Thanks for the answers. I put a sink drain in our new kitchen that is probably 10' from the nearest vent. Did this a few years back before I found this site. If I had known of an AAV, I would have used one. Being on the first floor of a two story house, and with no vent nearby, that would have been a wonderful answer. As it is, we live in the county with no applicable code, and it seems to work fine, but I do wish I had known of the AAV.

What county and state are you in? No matter how remote I always run into a local building department even if its at the county level where you know they will never inspect. Much of the stuff done out of code works fine but may not pass an inspection if you sell. Not too late to put that AAV in, if its code by you.

Rural county in Mississippi.

If you want this to be code and never haunt you during a future sale call the county building department and ask what codes apply. I assure you, there will be some code applicable to your area but maybe no inspector to enforce it.