Never pump out completely.
A major issue with boat holding tanks is most cannot be pumped out completely. The suction tube does not go all the way to the bottom of the tank leaving about 1 inch or more of sludge to accumulate. Few boats have a bottom draw that would empty completely at the right angle and a few have a side draw, but the moment the pump sucks air the pumping is over leaving that same inch or more of sludge. The historical solution has been chemical deodorants, but because they are diluted with every flush, they have a very limited working life in a tank and more deodorant must be constantly added. Most enzyme and simple bacteria digesters use a deodorant also.
With Forget About It For Boats in the holding tank it is no longer necessary or desirable to pump out the tank completely or back flush it. Because it is a consortium of 14 to 17 living and multiplying bacteria the only end of working life is when the job is done and the tank is clean. As long as there is food present they will continue to consume the solids and odors leaving behind only a near clear antioxidant and sugar based liquid. That is why we stress USE YOUR HEAD. These microbes need to eat too! Forget About It For Boats is the prefect solution to an ancient problem.