I want to add a sink between my washing machine and dryer. The washer drains into a fixture that has hot and cold water and a drain all in one box. If I cut into the pvc drain pipe below that and run a p-trap to the new sink do I need to install a new vent? If so does it go just after the p-trap? A new vent would be difficult as I have to open the wall and the new vent line would be exposed. I believe there is a venting gizmo that I could install instead. What do you think of that idea? Thanks - newplumber

Hey NP...

Unfortunately, you need to install the vent. Depending on where you live you may or may not be able to use a mechanical vent (as you suggested)... see picture below.

This mechanical vent (An AAV (air addmittance valve)) will need to be piped so it is readily accessible (as you also suggested by saying you would not need to open wall as much... correct).

This vent will need to be installed AFTER the trap and should rise at least 6 inches above the trap (I run mine up to 48" off the finished floor... but not required here).

Best solution, of course, would be to run an individual vent and connect it back into the washer vent at 48" off finish floor... but a bit more work involved here... for sure.

Mechanical vents can fail... but not all too often, so may work well here..?

Let me know what you think...

MARK
.

Thanks for your quick response! I guess I will go with the AAV. I believe that I need to install it on a 6" stub just after the p-trap before entering the sanitary tee which I will cut into the vertical waste line coming down from the washing machine drain. Have I left anything out?

Nope...you got it dead on.

:)

Do you have a vent for the washing machine drain in proximity to the drain. If so why can't you cut into the vent with a
Sanatary tee with a short stub in each end (top and bottom) then insert the tee into the vent, where you will cut out enough space, using fernco adapters. Then connect the sink into the tee you installed.

Do you have a vent for the washing machine drain in proximity to the drain. If so why can't you cut into the vent with a sanatary tee with a short stub in each end (top and bottom) then insert the tee into the vent, where you will cut out enough space, using fernco adapters. Then connect the sink into the tee you installed.

Letmetellu,
Did you miss this by the asker?
A new vent would be difficult as I have to open the wall and the new vent line would be exposed.
Also you neglected to advise the asker to iinvert the tee coming off the vent stack and pitch the vent line back to the drain. All important steps when you're reventing. I would also use shielded metal coupling in place of Fernco rubber couplings. They give the pipe ridged connections that a Rubber coupling can't
Massplumbers, (Marks) advice was bang on. Regards, tom

To Letmetellu: I guess I wasn't clear. I am installing a sink cabinet (from Home Depot) with an integral sink and faucet between a washer and dryer. They are plumbed to an 'all in one fixture' - a square plastic box with hot. Cold and the top of a s-trap (which is open to the air). The drain hose of the washer just fits into the opening. I plan to move the washer and dryer apart and open the wall directly below the all-in-one. The hole I cut will be covered by the sink cabinet. I am praying that the 1/2" hot and cold come up directly from the concrete floor (as does everything else in the house). I will cut the vertical drain line and cement in a sanitary t. Then I will tap the hot and cold with t fittings to new shut off valves and to the sink. I was originally hoping that because the vent setup is effectively the vent pipe PLUS the fact that the all-in -one is open to the air that I wouldn't have to install any drain. I was advised by Mark that to keep code, I need an AAV which I will install 6" above the p-trap INSIDE THE SINK CABINET. This will accomplish two things:
It will make the AAV accessible for declogging AND IT WILL ELIMINATE THE NEED TO
OPEN THE WALL ABOVE THE SINK CABINET. As I don't expect the sink to have very heavy use, I believe the AAV will suffice. Thanks to all who were kind enough to reply and I will observe this thread for any other advise you wish to give. - Newplumber

New plumber, Here's how it goes. (see image) Good luck and follow Marks advice. Tom