I bought mine with the intention that they turn the sand bed over. They (he) got a lot of food out of the bed but he will also sift food out of it that lands on the bed on occasion. He definitely likes eating food right out of the bed, though. Mine has grown very large and is probably about 5-6" in length now. I do miss seeing the pair swim and sift together, though, so always on the hunt for the second one.
As far as them dumping stuff on corals, etc, they certainly will dump it on anything that is in the lower 4-5" of the tank. I don't put much of anything on the bottom of my system, and my tangs are constantly "dumping" (pun fully intended) sand as they excrete waste which settles on everything. I have tons of flow, though, and the majority of this ends up back on the sand bed. For reference, my tank is 300 gallons with a 7'x30" footprint, minus of course the 3/4" acrylic. The bed is probably 50% covered by rock. For flow I have 3 Reeflo Barracudas - 1 on a closed loop that simply runs, 1 on a closed loop going through an Ocean Motions 8 Way, the other is the return from my sump. My tank probably turns over about 10,000 gallons per hour based on the barracuda being rated at about 4300GPH, so it "turns over" in excess of 30x per hour, so the sand doesn't settle much.
As the sand gets used to being sifted, it gets heavier and settles down very quickly.
I would also agree that in a 65 gallon tank, it probably won't last very long. They have the reputation for wasting away, especially when kept singly.
