Re: The Geo Method / Black and Gray Water Holding Tank Actually, for most of us, the solid waste doesn't stay in the tank long enough to need "breaking down" with chemicals. It isn't a septic system. It is a storage tank. The chemicals can only hope to deodorize your system until you dump it. The object of all of these two methods, Geo or just lots of water, is to make it harder for the solids to stick to the inside. That way they get flushed out during the dump. Did I mention that most RVs don't have 'septic systems' installed? Just storage tanks.