Adding washing machine drain to second floor 3" stack vent -please help?????

Can anyone give me advise on this.

We are adding a stacked washer and dryer the the 2nd floor (upstairs) of out 2 story house. I opened up the linen closet in the hallway and framed a larger space for the washer and dryer. This closet is by the back wall of our bathroom. When I cut open the drywall I located a 3" pipe which comes up from the toilet drain and goes straight up to the attic. It's pretty much right behind the toilet. My question is: can I tie into this 3" pipe with my 2" line. I would add a 3"x2" T. My concern is that it would be just above the toilet. Will this effect the venting of the toilet. Can I add an AAV to vent the 2" drain, as the fixture will be 5 1/2 feet away from the 3" stack. Any clarification would be appreciated.

Moderator note: merged duplicate threads

That should be fine as long as there are no fixtures connected to the stack above the washer drain. Of course the washer drain will need a trap. No other venting will be required.

I would be very concerned that the pumped discharge of the laundry would affect the trap seal of the toilet. I have heard of this very thing happening from people I trust.

To do it properly, you will need to tie into the stack below the attachment point for the bathroom.

phishfood said:

I would be very concerned that the pumped discharge of the laundry would affect the trap seal of the toilet. I have heard of this very thing happening from people I trust.

To do it properly, you will need to tie into the stack below the attachment point for the bathroom.

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Sorry phfish this is I think the first time I disagree with you. If the stack was 2" then there would be a slight possibility it could effect he toilet. But with a 3" stack it wouldn't happen.

John, have you had personal experience with tying a laundry into a 3" soil stack vent?

I have heard multiple accounts of having big problems with tying into a 2" vent, based on that I have always thought it a bad idea and would not recommend it. If you have personally done this several times and it worked well, then maybe I need to rethink my position on this.

I can say that I have done just that many times. Don't see it that often down here as most homes are single story. But up north were 90% of my work was new construction and most homes were two story larger homes. It was common practice to put the laundry's on the second floor where the bedrooms were. What I most also say is the clothes washers were not the same as the newer ones today. In fact the codes on laundry drains were just starting to require 2" lines.

You know, I have thought about this some more this afternoon.

According to IPC, which is the model code for Florida, this is technically against code. A wet vent for a bathroom can only receive waste from fixtures within that or another bathroom on the same floor, and IIRC, has a specific prohibition against fixtures with a pumped discharge.

But then again, a waste stack vent system with 3" pipe can serve 3 floors of laundries, something I have installed many hundreds of times without issue. So I don't think that this piping arrangement will cause problems, but it is against the code that I work under.