I've never actually tried biological washing liquid, but most other products, and a couple of them do work but, as I said, they cost a lot of money in the long run. I also don't want to fill up precious space in the tank with watered down solutions.
Shit stinks. Hence, probably, the expression "smells like shit". Calcium nitrate is probably the cheapest way to deal with that fact. An old t-shirt might do the trick for some people, but the idea of having litres of refuse sloshing around in the boat in an open container, very close to both the dining area and the sleeping area simply isn't a good idea in my book...