Consider an extreme situation: a fully opened faucet and a completely
closed pop-up bathroom sink drain. Should a properly installed overflow
opening actually prevent the sink overflowing? Or it is supposed to
just help the main [open] drain by lowering the about to overflow water
level down faster?
No, it's a "regular" one but the spring-loaded pop-up drain that was
included with the sink has been replaced with the handle-operated one
that came with the faucet. It could be that the internal cut (within
the pop-up body) that is made to accommodate the overflow stream is
What is the practice of marrying the sinks with overflow openings with
"non-native" pop-up assemblies to avoid such obstructions?
Generally the overflow enters the main drain just below where the drain
pop-up closes. Therefore if the pop-up is open and the drain is not
draining to the point the water backs up to the overflow, you are probably
out of luck since the blockage is probably beyond (down stream) from where
the overflow would connect.
In the old days, a fully open sink faucet could overwhelm the sink
overflow (I did the experiment in more than one sink)
but with the mandate for "low flow" faucets I'm guessing that
overflows might now handle the flow.
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