Venting a Pesdestal Sink

formarley · 06-07-2005, 10:32 AM

We have a 1930’s home where we are installing a pedestal sink into an old vanity bathroom on the first floor. Never having installed drains before, I am not certain on how I should proceed as far as hooking it into the drainage system of the house. I have spoken with several folks, and I realize that the sink must be vented.

The question I have is, is it possible to tie the sink drain into the existing stack vent of the house? Given the location of the bathroom and other drains in the house, this is the easiest place for me to go to. I know I could install an air admittance valve, but since it is a pedestal, it will be a little unsightly (also, putting the AAV in the wall is not option – too much plaster to break into).

From what I have read, I think it is O.K. to tie it into the stack. However, one more thing about it is, there is a bathroom directly above that also ties into the stack. Would this at all prevent me from tying in the pedestal on the first floor? Thanks!

MinConst · 06-07-2005, 08:35 PM

I am going to let this one be answered by a plumber but I do know you don't want to put an AAV inside a wall it is against code.

Scott_K · 06-08-2005, 02:39 PM

Not a plumber here, but these are my experiences.
I would think it would be normal to tie it to the existing stack. I had a new bath put in on the second floor. They extended the existing stack and tied it into that.

If I understand correctly, the AAV is one of those pieces that allows it to vent without having to run a stack to the roof......correct ? I remember there is a certain height minimum where it can be mounted. I'm guessing that you wouldn't want to put it in a wall because it needs some free flowing air when the valve opens up.

formarley · 06-08-2005, 05:32 PM

My only conern about tying it into the stack is the fact that on the floor above this bathroom, there is a full bath that also ties into the same stack. Would there be any limitation using the stack when it is also used in an upper floor?

MinConst · 06-08-2005, 08:33 PM

There is no problem using the stack for drainage. It is your main drain. All drains will go there. The only issue is the venting of this new drain. It is possible that the new sink drain could suck the water out of the upstairs traps. Allowing sewer gas to enter the room. You really want to consult a licensed plumber about this. There are AAVs that will fit right in front of the drain after the trap on the new sink. If you have the room it wouldn't even show. Stop at a plumbing supply and look at the options on AAVs you might be surprised.

formarley · 06-09-2005, 01:17 PM

Another Quick Question:

Has anyone had expereince with this? There is a product put out by Watts Brass and Tubular called an "Anti-siphon S-Trap". Of course, it is an S-Trap, but the trap is designed a little differently. I found it at a local hardware store. The guys there say I can use it in the place of an AAV. (here is a picture of a P-Trap with the same weir design) Thanks!

MinConst · 06-09-2005, 08:36 PM

I don't see how this would replace the need for a vent.

Tomm · 06-12-2005, 12:58 PM

If the drain is attatched to the main drain line directly, or indirectly, there is no need to vent the system any further. The drain works off gravity and atmospheric pressure. Water goes into the basin, down the drain. The vent prevents any vacuum, or suction to draw trap water out of any other drain. When the weight of the water in the sink stops forcing it past the trap under the sink, the main vent will allow air in the line to fill the void at the trail end of the drained water. If the vent is not in position to do this, call a plumber so he may engineer the proper ventilation. If it is not done right, it will cause some real headaches.

formarley · 08-08-2005, 04:46 PM

Thanks for the advice! I put the sink in, tied the drain into the vent stack about a month ago and have no problems with it. I used a flexible tee (3") to tie the drain into the vent. It reduces to an 1"1/2 to connect up into the s-trap. I spent more time driving to and from the store buying the parts than fitting the pipes together.