Skimmer location in sump?

[easternreefer]

First time having a sump. 20 gallon long.
First section 17 inches long. Drain is here
Second us 4 inches.
Last is 9 inches return pump us in this section

Which section should the skimmer go?

 

[landlubber]

personally i would use chamber 1 for all my equipment just to allow any bubbles time to settle out before hitting the return

 

[Ty Hamatake]

The only requirement for which chamber the skimmer goes in is that it fits ;) I would also go with one that has a constant water level (i.e. not your return chamber).