I was having a similar concern in one of my nanos. It houses a mantis shrimp, so the cleaning crew will inevitably be short-lived.
I tried something new tonight: I put a short length of PVC over the powerhead in the sump (using an elastic band as an O-ring), and filled it with a fine filter media. I then used a turkey baster to blow all the crud off the rock. With the attachment on the powerhead, the water clears up within an hour or so (as opposed to overnight without it). After three blasts over the course of the evening, the crud in the tank was very noticeably less. Tomorrow I'll take off the PVC attachment so it doesn't become a nitrate trap, then I'll just siphon out the bottom of the sump.
Too easy.
I'm sure this could work on a larger tank.
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