If you're doing your weekly water changes, then you should be siphoning the left over bits on the bare bottom at the same time! I keep my tanks "bare-bottomed" and can clearly see want needs to be siphoned up! That's what I use for "cleaners"!
I do siphon the bottom every weekly waterchange but it takes too long and left over shrimps are usually found under driftwoods. This left over food add nutrients for algae to grow on the bare bottom and make my bare bottom all brown. You see this where clown loaches or bottom feeders come in handy. They will get into the crevices at night to eat the left over. So far I'm thinking of gettng some loaches only if they don't scratch up my acrylic tank with their spikey whisker.