sink drain into standpipe modification

Hi All,

I'd like some opinions on a DIY project. Currently I have top loading w/d setup. Upgrading to a front loading w/d setup that I'm going to stack and a new laundry tub.

I would like to complete the modification shown in the attached picture. Plumb a 1.5" line for the laundry tub into the standpipe.

Can I use the standpipe for venting the laundry tub? I'd also skip a p-trap for the laundry tub, since it would be using the standpipe trap.

The nearest vent after the trap is a nearby wc approximately 15' away.

The standpipe is 2", approximately 40" from the trap.

Only one trap per fixture served. So .... NO

geniescience said:

How is this standpipe vented at this moment?

I think under one of the codes, it is permissible to have a washer and a laundry tub on the same trap. ----

Click to expand...

After the trap, it basically isn't vented. It's a long 2" horizontal run then 90s down to the house main. I don't think it's siphoning the trap since we've never smelled sewer....Hoping the higher discharge rate of front load washers or the addition of a tub doesn't create any problems. Wondering if anyone else has been in this situation before I make a final decision.

The washer needs to be vented within five feet of the trap.
The trap for the washer needs to be on the same floor as the washer, not below the floor.
If the riser is too tall, that will siphon the trap.

Wondering if anyone else has been in this situation before I make a final decision.

Click to expand...

I have and it ended up being a whole lot simpler discharging the washer in the utility sink.

Without repiping it simply is not possible to keep a utility sink and a washer.

If it was that easy, I would have done it long ago.

Design modification

Yeah, I'd prefer not dumping into a tub...

and I figured hoping for the best isn't a good idea when stuff gets closed up behind walls so I decided to vent it (see revised drawing). Going to install the new standpipe with trap on the same floor, run it to the next stud space where it will go into a 2" santee and down and over to the house main. I'll plumb the utility tub drain over with 1.5" and into a 1.5"x1.5"x2" santee stacked on top of the standpipe santee. This stack will vent.