Venting lavatory sinks
Posted by Phil on March 20, 2004 at 12:44:30:
I am remodelling my bathroom and the position of the vanity basins is to be moved. I thought I could just drain the new basins into the same drain that the shower and bath go into but looking around your site it seems that this is more complex. I had never heard of venting until I checked out your site! Can someone advise me on how I should do this?

The bathroom is on the top floor. At present the bath tub drain runs about 10' sloped horizontally, the shower drain runs about 5' - they both are 1 1/2" ABS pipes which join in a Y into a 2" drain which has a 2" vent pipe to the roof which eventually T's into a 3" pipe out through the roof (many other 2" and 3" pipes T into this as well). The existing vanity basins have their own vent pipe but I can't get to this because of the joists.

On the same wall that the new basins are to be installed there is another 3" vent pipe but I am not sure what it is venting as there is no bathroom beneath this.

So my questions:
1. Is it ok to run the new vanities into the same drain as the bath and shower?
2. Do I need a new vent?
3. Can I T into another vent pipe or do I have to run a new pipe to the attic and T into the 3"? Cutting the holes for a new pipe will be very difficult so I would like to avoid this.
4. If I have to run a new vent should it be 2"?

Hope you can help,

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