Why is it when one side of the sink is plugged, the other side sometimes won’t drain even if there isn’t a plug?


I’ve seen this in a bunch of different sinks, if they’re two different pipes, how does the pressure change from one side affect both? Say I’m doing dishes in the right side of the sink with it plugged and rinsing the dishes in the left, unplugged side, the water that’s in the left doesn’t go down until I remove the right plug. They’re not the same pipe for a bit, how does the pressure from the right keep the left from draining?

In: Physics

The two side by side sinks you’re describing are usually on a Y shaped drain (both drains are going out the same place a little further down). There are several places on the Y that a clog could form but if it’s at the junction or the leg (assume the anatomy of a drain is like wacky-arm-waving-inflatable-tube-man) then both arms will back up.