I've always pondered this too...
With my leo of 17 years, I use to just remove everything from his tank, place it in a sink, and run scalding hot water over it all. This pretty much eliminated all dirt and smell. As for the tank, I've always done regular maintenance on my tank to keep it neat and clean. But when I empty the tank out for deeper cleaning, I use a standard antibacterial counter cleaner (Method), sprayed on a paper towel (not directly into his tank) to wipe his tank down, and then after that I take wet/hot paper towels and wipe it all down again, to get rid of any smell left from the cleaner. Then I let it dry for a couple 1/2 hour til there is no trace of any cleaning smell. I don't know if other people use this method, but it's worked fine for me for many years, and my last leo didn't seem to be affected by it.
I guess if I suspected any disease or bacterial infection in my leo, I'd go an even deeper route cleaning (bleach or ammonia...etc), but for just cleaning the usual dirt, the method above has always worked for me. I'm interested what others think of this???