I am connecting a washer standpipe trap arm to a drain.

From the trap, the pipe will run a few feet to a vertical drain/vent. That drain/vent also serves as the drain for the laundry sink (which connects just above where the standpipe trap arm will meet the drain vent) and, above that, a vent for the sink in the adjacent bathroom. I will run a separate vent off the standpipe trap arm, before it meets the vertical drain/vent. This standpipe vent will reconnect with the drain/vent above the other vent connections and above the flood level of the washer.

Question: I understand that a sanitary tee (insted of a combination wye and 1/8th) should be used where a trap arm meets a vertical drain/vent, so that the vent does not get choked off by the water flow from the fixture/washer. But is this true even if the washer standpipe is separately vented before meeting the drain/vent?

If not, it seems like using a combination wye would be preferable to the sanitary tee, since it will better direct the strong discharge from the washer.

Thanks for any thoughts!

AMWASH:

I say that in this case you can use either fitting.

In fact, as you presented it, I agree that a combination wye fitting may be best here.

I recommend 2" pipe and 1.5" vent. Install a 2" ptrap and make sure the pipe coming out of the trap (the washing machine tailpiece) is at least 30" tall.

I also recommend a full size cleanout (called a dandy clean out or a TEST tee fitting... see picture below) be installed just after the combination wye, but before the vent or trap... OR you could also install a UNION ptrap (see other picture) that will allow you to drop the ptrap should you ever need to snake the drain line in the future... ;)

Good luck with it all. Let us know if need more info...


MARK

Great. Thanks, Mark.

The vertical pipe for gray water drops from the laundry room into an unfinished part of the basement, where it ties into the main waste stack. Would it be better to put the cleanout in the basement, before the tie-in to the main stack? That would give easier access (and avoiding the need for an access panel in the laundry room wall). What part of the drainage set-up am I trying to give access to--the trap arm or the combination wye?

Also, should I use teflon tape on the cap for the cleanout?

Thanks!

Yes... put the cleanout where it is readily accessible. I would install it just before the tie into the main stack.

The teflon tape is correct... go 6-8 wraps on a cap... ;)

Good luck!

MARK