I do a water change once a week, where I do a through vacuuming of the substrate (mine is gravel). Between cleanings, if there is visible poo on the surface that the filter doesn't suck up, I go in with a quick vacuum. I probably do the quick vacuum once in between water changes, maybe twice. The quick vacuum only takes a few minutes and probably only removes a few gallons of water - which I then treat with Seachem Prime and replace.
I can't stand having visible poo in the tank - I'm very fussy about that. It really shows up on the black gravel - in my old tank I had multi-colored brown gravel where the poo didn't show up as much.