We are going to talk about poop pyramids. Sorry if that brings on a gross visual. Poop Pyramids is what happens in an RVs black tank when solid waste builds up. Why does this happen? The short answer is that that ratio of liquid to solid waste in the tank is too low. Reasons this could be the case include that the valve for the black tank has been left open all the time allowing liquids to empty through the sewer hose leaving the solids behind to build up in the tank. This can also happen when the valve is closed simply because there is not enough liquid.
How can the poop pyramid be prevented?
We do several things to keep our tank pyramid free. The first is using chemical for the tank that helps to break down solids along with a bed of water in the bottom of the tank to help activate the chemical. In addition, when our tank is roughly half full we will fill the toilet bowl with water a few times and flush it down. This does use a good amount of water and we only use this method when we are at a full hook up site. Or alternatively we will fill a dish basin with water and pour it down the toilet. The idea here is to keep the liquid level in the tank higher than the solids level. That way when we open the valve to empty the tank we get a nice whoosh which hopefully empties the tank completely.
Rohdsteading 