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:
(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.
I thought they had to use a "double fixture fitting", slightly
different than a double sanitary tee. Like this one:
That would certainly prevent the problem. The house was built in 1969,
so maybe it wasn't required back then.
In response to others, the water flowed out the open trap even with
modest amounts of water running in the other sink from simply turning on
one faucet. In other words, I didn't fill one sink then try to empty it
quickly by raising the popup suddenly.
Now that the p-trap is reconnected, all is working properly.
Thanks to all who responded.
If the pipes are sized and vented properly this should not happen even
though it can. In your case, the open P trap is lower than the basin so it
is certainly more likly than otherwise. In fact, the bottom of the P trap
is lower than the connection to the drain, the flow may be inevitable,
there's no uphill, just a short 2" hop across the pipe.
You may want to just run a snake down the drain from both sides just to make
sure there is no partial obstruction slowing the flow and waiting to clog.
Good idea to do this once a year or so with bathroom drains. hair and
personal products clog drains fast and bath sink drains are often only 1.5"
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