First and foremost, the tank on the camper is NOT a septic tank. It is simply a holding tank used to collect waste until it can be dumped into a septic tank or a sewer system. Water (and lots of it) are usually all that is needed in the holding tank. Some use a chemical deodorant such as what your mother bought to help with the smell of tank, which should not be there in the first place if enough water is used when using the holding tank, and the tank is emptied often. The valve on the holding tank needs to be left closed all the time except when emptying the tank, otherwise liquids will drain off and solids will build up. You need to rinse the tank thoroughly with a hose, a rinsing wand, etc and hope the build up is not too bad and will break down and rinse away. Be sure that she understands to leave the tank closed except to empty it as needed.
