If they are installed with a "cross" or "X" fitting in the wall, likely
water will gush across the opening and come out the open trap on the other
side of the wall.

"Ray K" wrote in message
...
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?