Protein skimmer in a sump

Ok time for a dumb question. When a protein skimmer is in a sump, the clean water it expels, does it just fall back into the section of the sump the skimmer is in? Or does it expel it to a diff section? Just doesn't make sense to me, bc then it could try to clean the water it has already cleaned. Or does it not matter bc the flow coming from the overflow will push the clean water to the next section? Sorry if that's confusing...

 

Water is flowing into the skimmer section, and out of the skimmer section. The skimmer itself is pulling in, and letting out, a portion of that water. So, yes, the way you're thinking is the way it works, but the flow through the skimmer section is usually much higher than the flow through the skimmer itself.

 

Got it, so it doesn't matter if the skimmer is releasing water back into the same section. I have a 29g tank that I'm thinking about turning into a sump/fuge so I'm just trying to figure out how sumps work. thanks