Garbage Disposal Plumbing: Weird Things You Didn't Know

That’s useful to know, but I wouldn’t treat the overflow as protection against an overflowing sink: if the faucet is running faster than the overflow can carry water away, the level can still rise. It’s more of a backup path than a guarantee.

That built-in trapway has a small follow-on surprise: after a flush, the tank’s refill tube sends some water into the overflow tube, which helps replenish the bowl and its water seal. It’s a neat reminder that the toilet’s odor barrier depends on water in the fixture, not a separate under-sink trap.

The refill-tube detail surprises me more. The trapway’s water seal makes intuitive sense once you picture the curved passage; I wouldn’t have guessed that a small stream from the tank helps restore that seal after every flush.