I have a finished basement with an unfinished basement bath. It is plumbed under the slab to a standard sewage basin. The problem lies in venting the basin if I wish to finish the bathroom and install a sewage pump. I do not have access to any pre-existing vent stacks, but do have easy access to the main drain line.

I realize I can't use an AAV due to the closed system, but is it possible to vent to the top of the main drain line? The line is never "full" unless there's a downstream backup (yet to happen). Wouldn't this essentially be the same as venting to the vent stack?

First question, would this work... Second, would it be against code...

Thanks in advance

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Originally Posted by ;

I realize I can't use an AAV due to the closed system, but is it possible to vent to the top of the main drain line?

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What you have under the slab should look something like this, (see image).
You may use a AAV on the lavatory, ( check with your Building Department) but the pit vent MUST be a dedicated vent that may be revented back into a existing roof vent in the attic but not before. Good luck. Tom

Thanks speedball...

I figured this was the case. Could I bring the vent line straight up into a joist space, turn 90 and vent out of the side of the home? There are no windows or doors on that side.

If no, then I'll begin pulling drywall next week...

p.s. the toilet dumps directly into the pit and is only ~36" away. I'm assuming I will not need to vent that. I plan on using a AAV under the vanity for the sink. Does all this sound kosher?