Installing trap in washing machine drain pipe

We're getting a sewer smell from our washing machine drain pipe, which I'm assuming is because we need a trap. Should it be installed above the floor or is it possible/advisable to install in the crawlspace (please see pics). Also from what I've read we need a vent. Is that what is labeled in the second picture? If not, where and how should that be installed?

House is in Indiana and was built in the 40's.

http://i1156.photobucket.com/albums/p561/larrylbryant/4_zpsxee8mdot.jpg

http://i1156.photobucket.com/albums/p561/larrylbryant/1_zps84dq650w.jpg

http://i1156.photobucket.com/albums/p561/larrylbryant/2_zps1cjy6kwx.jpg

http://i1156.photobucket.com/albums/p561/larrylbryant/3_zpsiovyss7d.jpg

Well it looks like a lot more work doing it from the crawl space . I will do it from the top add a p trap sanitary tee and aav on top

Okay I googled and figured out an aav is an air admittance valve (I know next to nothing about plumbing). Would something like this be the correct configuration?

http://remodeling-projects.com/img27.jpg

The house may have been built in the "40's, but that was handyman-hacked in much later, probably in the 90's. I would consider calling a plumber in, as I am thinking you have problems with more than just the laundry.

DoNotMistakeMeForAPlumber said:

Okay I googled and figured out an aav is an air admittance valve (I know next to nothing about plumbing). Would something like this be the correct configuration?

http://remodeling-projects.com/img27.jpg

Click to expand...

Something like that. the one in your photo is to small.
Use all 2"
remove that AAV you have under the floor and cap that wye.

Cut the stand pipe about 6" off the floor and glue on a santee and add a 2"trap with a 4' stand pipe in the trap. best to bring the AAV up as high as the stand pipe.

I think that pipe is 1 1/2".....

It all needs to come out and be replaced.

Wow okay thank you so much for all the helpful replies.

phishfood said:

I think that pipe is 1 1/2".....

It all needs to come out and be replaced.

Click to expand...

Good Eye. Closer look it says 1 1/2" on the fittings.

If it takes the water okay now, adding a p-trap might NOT do as well.

Auto washer drains should be 2"

1 1/2" washer drains were fine for years and years and years. Just like anything, if its thought out and piped accordingly, it will work. Although the code now is 2", theres no need to tear it all out and go 2". If it currently does not have a trap, you can put an 1 1/2" trap on it with an 18"-24" stand pipe

Matt30 said:

1 1/2" washer drains were fine for years and years and years. Just like anything, if its thought out and piped accordingly, it will work. Although the code now is 2", theres no need to tear it all out and go 2". If it currently does not have a trap, you can put an 1 1/2" trap on it with an 18"-24" stand pipe

Click to expand...

I agree. I was saying it MIGHT not do as well only because adding a trap may slow down the flow a little. newer washers have better pumps in them than back in the days when 1-1/2" was okay.

New washers use less water too!

So, has it even been determined there's no trap here? Definitely don't want 2 traps on there

It looks like there are other fixture draining to it as well. From what I can see, there is no trap. The AAV is a cheapie, and is underneath the house, where it can release sewer gas or leak without being noticed. There looks to be pressure fittings in parts of the drain line. It could use more and better support. Regardless of what worked for years, IPC requires 2" fixture drain with a 3" stack or branch drain for a washing machine.

If I were to go under a customer's house and see this piping, I would recommend complete replacement as the only proper fix.