Newbie Diy-er NEEDS HELP w/ laundry drain

[timintx]

I'm brand new to this site, just hoping to get some tips from the pros!

You may need to look at my microsoft paint drawing to understand my questions
http://s15.postimage.org/tn02flxg9/Laundry_room_plumbing_diagram.jpg

Anyways, I bought my house about a year ago, shortly after moving in, we found... that water leaked out from under the baseboards behind the washing machine in the laundry room. So I tore up the wall and found that the the copper to pex fitting on the hot supply side leaked water every time the valve was turned. At the same time there was a gap where the iron to pvc rubber fitting had not been attached properly. I fixed those issues and closed the wall back up. I figured that the trap must be in the slab and I figured there must be some kind of vent... somewhere maybe.

Now my problem is... that I get sewer gasses in the laundry room. They seem to be coming from the drain, which probably means I've got no trap in the slab(i don't really know if that was ever done for laundry) The house was built in 78 so I don't think I'm the first one to go behind the drywall (I don't think Pex was very common in 1978), there may have been a trap at one point but not anymore.

Is there anyway that I could fit a trap and vent(maybe a recessed aav with a grate cover above the connections) and can this be done without moving the connections?

FYI it's a first floor laundry room on a slab foundation

 

[phishfood]

Here is a picture of a laundry drain that I piped in last weekend. Notice the offset under the tee, 4" length of pipe between the tee and the trap, the vent continuing horizontally up from the tee. While an AAV is not my first nor my second choice method of venting, it has it's place, and might be the only practical choice for your situation.

 

[IFIXH20]

Many older homes have traps under the slab at the laundry drian. I think you need to find out if there is a trap under the slab. The trap could be broken, the vent could be crack -- find the source of the problem before making any repairs, have a plumber out to find the problem if you can't find it. You may need a smoke test.

 

[timintx]

Just in case the drawing isn't showing up
http://s15.postimage.org/tn02flxg9/Laundry_room_plumbing_diagram.jpg

@phishfood That laundry plumbing looks great. If I can leave the connections in the same spot though, it'd make my life easier. Could I jog over one way or the other with the p trap, run a vertical vent at the end of that and then jog back over back to where I started? Like this http://www.freeimagehosting.net/fc48v

@ifixh2o, if it drains well currently, couldn't I just add a trap and vent up stream of the potential current one?

Thanks all

 

[phishfood]

It is not good practice to install two traps inline on a drain.

If there is not a trap already in the floor, then yes, you could offset under the new P trap, similar to the picture I posted.

But I start to get worried when I hear about steel pipe, that starts to open up other cans of worms that can be difficult to diagnose or deal with.

 

[IFIXH20]

Two traps could possibly cause the drain to overflow when the washer drains in spin cycle and/or cause the upper trap to sipon or break it's seal. Take a piece of 1/4'' or 3/8'' X 5ft tubing (pex/polly), tape a rag to tubing then push tubing down laundry standpipe if rag comes back wet you have a trap -- you can also try dropping a dime down standpipe while listening for a splash when dime hits trap -- These will only work if trap is directly attached to standpipe.