Correct and thank youThat's looks to be his returns. And the overflow is shown in the first photo at the end.
@prsnlty your tank looks amazing. I'm about to give this a try but one question is, due to the cement is the rock very heavy?
To answer your question... the rock is heavier the less porus you make it. Also. My overflows are actually kind of ligh as they're made of 6" pvc pipe, coated with netting then layered with rock mix not quite an inch thick. This is pretty much true for the return column as well. Only I made the mix more dense with more sand because i needed it to fill in the narrow ridges better.
I had promised to do a diy on it but you know how life goes... still hoping to find the time lol