On Sat, 22 Dec 2007 12:54:38 -0800 (PST), buffalobill
wrote:

On Dec 22, 11:35 am, Phisherman wrote:
I'm installing a double sink. The basins are 20 gallons each and the
drains are about 8" apart. I will be installing a 1.5" PVC vent
around the room near the top of the studs to serve all the fixtures.
There are two ways to connect the sink drain--a single trap or
separate traps for each basin. If I install separate traps, I could
install a separate vent for each trap. I want to eliminate any
possibility of waste water draining from one basin to enter the other
(empty) basin. What is the best configuration?

buffalo ny: who/what/where/when/why/how:
who is stopping you from reventing to the 4" soil stack?

There is no 4" soil stack.

what is the trap size don't go bigger than the kitchen 1-1/2" or the
draining will fight an oversize trap.
where are we, in the kitchen?

Basement.

when you run all the fixtures simultaneously in the house thru a slow
sewer
why not check the local requirements, sometimes for the cost of a
plumbing inspector will get you amazing info to help you.
how far above/below grade, how much water is pumped out so much faster
on many of the newer machines, how much pitch is needed on your
upcoming addons and so on.
first look at:
http://www.free-ed.net/sweethaven/Bl...p?iNum=fra0309
second, see good vent specs at:
http://www.oatey.com/apps/catalog/in...tion_Sheet.pdf
general description info and links at:
http://en.wikipedia.org/wiki/Plumbing_drainage_venting
and see:
http://www.theplumber.com/index.html

Thanks for these links.