I'm a sort of a predicament. I plan on installing utility sink in my garage. It's up against the finished wall and directly on other side is water heater, and 4" sewer stack pipe. Now I piped my water lines, now I'm tying to figure out the proper way to splice into the sewer line and vent the sink drain! Any help would be appreciated

what material is the 4 inch pipe?
as for the vent, you either run a pipe thru the garage roof (away from any windows) or if allowed you use an air admitance valve (AAV)

The sewer line is pvc sch 40. I can't go straight up because house is split level and bedrooms are above garage

I'm no expert, but without a photo to look at it seems like you can just splice in your sinks trap arm with a san tee and appropriate reducers and be done. If the sink is really right on the other side of the wall. is there a height clearance issue? I wanted to do something like this before but there was a cleanout in the stack right where I wanted to splice in...

This is probably the drain line from the upstairs bathroom so he CANNOT just "put a tee in the pipe" and be done with it.

It's my main sewer drain for both bathrooms upstairs. Kitchen sink is on its own, it being main one is why I'm stuck on it

[goo.gl]



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you can 'splice in' but you will need to vent the trap.
if an AAV is legal in your area then that will cover the code.
cutting a san tee into the stack is difficult because you have no up and down give to the pipe. probably have to use a couple of rubber couplings to slide up and down. i know they aren't supposed to be used indoors but in this situation i have risked burning in hell and done it with them.

An AAV might cover the code, but it won't cover the physics. An AAV only protects negative pressure, water falling down the stack will create positive pressure. Protecting the trap would require a vent.

How does positive pressure siphon a trap? Assuming the main vertical stack is already properly vented, yopu only need this fixture vent to prevent the trap from siphoning, and an AAV will do that.



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A positive pressure will move the water upwards in the trap slightly and if the trap is unvented the negative pressure behind the water will suck the water towards the trap outlet. the combination of the two will syphon the water.
but if the AAV breaks the negative pressure then the positive pressure might affect the water in the trap but it will do no harm.
if there is a concern, use a regular street 90 instead of the trap street 90 to give you about an inch more water.

[www.youtube.com] For Don.

Good video, thanks, and that's the way that I understand venting to work. I was questioning Tom's post above where he is saying that even installing an AAV won't stop the trap from siphoning because of the positive pressure that's created?