Quote:
Originally Posted by cmac2012
Oh good, a little more affirmation helps. I'm starting to get the part about why plumbers pay major $$ for liability insurance.
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You're typically running 1 1/2" for the vanity from the wall to the 2" or 3" drain line. It's virtually impossible to fill that line more than 1/2 way due to the limitations of the vanity drain..........it won't flow enough water. So, there is always the upper part of the line to allow air to return from the main vent.
If you somehow managed to fill the 1 1/2" line.........then, you'd have drainage issues.