Try and do a little research into alternatives to the blue stuff. When I was managing an aircraft about 10 years ago I replaced the blue stuff with a clear additive to water which turned the human waste to jelly and stopped the smells. I am afraid that I can not recall what it was called. I filled up the tank with water and added a measured amount of the fluid as I was doing it. It turned the human waste to jelly which was suspended in the water and stopped smells. It also had the advantage that waste could be disposed of down the normal toilet system as it was not chemical waste.
MM