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How to Position a Vent Pipe
By: Danny Lipford 
My shower and washing machine drain need a vent pipe. Should I put the vent downstream from both of them or in between them? -Deb
Hi Deb,
Depending on the distance between the drain pipes for the shower and washing machine, you may be able to install one vent at the one further downstream to serve them both. The maximum distance recommended between two drain pipes for them to share a vent is 3½’ for a 1½” drain and 5’ for a 2” drain pipe. If they’re further away than that, each should have their own vent, though the two vents can join together before going through the roof.
If your codes allow, you may be able to avoid running another vent stack through the roof by attaching a one way vent known as an air admittance valve on the drain line. This allows air in while preventing sewer gases from coming out.
Good luck with your project,
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November 2nd, 2011 at 8:00 am
With my new high efficiency gas furnace it purges condensation from the air handler just like my central air unit does in the summer. My question is that during cold spells the water freezes in the pvc pipe when it exits my house. I have to thaw it out routinely to keep the line clear. I would like to avoid using heat tape to fix this. I am thinking of running the waste water pvc line straight into my plumbing vent line so that it doesn’t have run to outside of house where cold temperatures freeze the line. How do I bore into the vent line? Do I use a spade bit and then seal around connection with silicon caulk?