how does the plumbimg work in a rv?

Welcome to RV.Net, every coach since 1976 that I ever owned had two tanks: Black Tank that your toilet or toilets drain into and a Gray Tank that your sinks and shower drain into. There are meters inside the coach that show the different levels of waste or water inside your tanks (it will show you if your tanks are empty, 1/4 full, 1/2 full, 3/4 full or full) You empty them from a outside compartment. There will be two T-Type handles one is Black (Black Tank) the other is Gray (Gray Tank), next you hook your sewer hose to the tanks outlet (this is where the Black Tank and the Gray Tank meet and form a Y and drain into one fitting with a sewer coupling on it. The other end of this hose goes into the Campground septic tank. You always drain your Black Tank first, when it's empty then open your Gray Tank and your gray water will push all the material that is left in the hose from the Black Tank into the Septic Tank. You can drain your tanks daily or wait until there full it's your choice. Any variety store Walmart etc. will sell chemicals I buy the type that has no formaldehyde in it enviromentaly safe. If your dry camping (no water or sewer to connect) like out in the desert I have gone up too 2 weeks before (2-adults) dumping my tanks and yes there are companies that will bring water to you and come and pump out your septic for a cost. I hope I explained this to you so you will be able to understand? Also after emptying my Black tank and the outside handle is in the close position I use 1/4 cup of Dawn dish soap with 5 gallons of water and when I'm driving down the road it's slushing inside the tank and keeping the bottom of the tank clean.Good Luck.