Holding tank tablets. The microbes in the tank tablets consume the ammonia which causes offensive odors, and they break down organic solids so that the tank works more efficiently. Prevents crystal build-up in the pump-out equipment, adding another benefit to boat owner maintenance. The 3-gram tablet contains 60 billion microbes- a consotium of 100 species of aerobic, micro-aerobic and faculative anaerobes of the Archaea domain. Simply drop one tablet in your empty black water holding tank.