Ray K wrote:
I have two back-to-back bathrooms. Their lavatories are also
back-to-back, and the same distance from the side wall. If I run the
faucet in bathroom A while the P-trap in bathroom B is open (waiting for
a repair part), the water from sink A will run out of the open trap in
bathroom B. Is this normal?



Back-to-back fixtures are plumbed into a
Double Sanitary Tee, like this one:
http://tinyurl.com/44wyvs

(not necessarily this size one...)

Under low flow conditions, waste might not
cross over, but a sudden draining of the basin
might spill some out.



Jim