Clayton,
Not too many fish in your 29g, that's good
In our three BB tanks (37g, 67g, 120g), we left space around the sides and back of the tank where there is no rock so we could siphon the tank better. We also do the siphoning in two stages. First stage is siphoning the crud that's easy to get at, where it usually builds up at the back. Second stage is blow the crud from under the rock to the back of the tank, then siphon that stuff out once it settles, usually 15 minutes later. Powerheads are turned off and removed from the tank for cleaning before the siphoning begins. We do this weekly in all the tanks.
Also, the day before water changes, I clean the glass then turkey baste the rock and some of the corals. You'd be surprised at how much crud accumulates in the porous rock, and the tank gets kinda cloudy. Some of the crud is picked up by the mechanical filters in the tanks, some drops to the bottom of the tank, and then some just falls back onto the rock, but at least we're getting as much crud out as possible this way.
HTH.