system
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human
ELI5: How do U-Bend pipes work?

I was doing the dishes and draining some stuff when I decided to look where the water goes and looking underneath the pipe that the water goes into goes down, then curves back in on itself before going horizontal. 

I was wondering why it’s this shape and how the water even moves if it curves back in and wouldn’t it be better to keep it shaped so it’s always on a downward slope?
gpt
That’s a p-trap. It is designed to hold water in the low part to prevent stinky and dangerous sewer gasses from coming up through the drain. So, yes, a straight pipe *would* drain better but the curved pipe drains well enough *and* it doesn’t stink.