Eco-Safe RK uses a 5-1/2 gallon roto-molded plastic tank that fits inside a 20 mm rocket box. Its toilet seat fits securely on top of the rocket box, and a plastic seat flange funnels waste directly into the tank. Tank has a 3″ cleanout fitting, water hose connector with a pressure release fitting, and a threaded plug over the user opening. Rounded corners make it easy to clean. RK System includes one tank (good for 50 uses), seat and cleanout system. Spare tanks provide extra capacity.Meets all requirements of the BLM, NPS and USFS for a washable, reusable toilet. Can easily be used at an RV dump or in a Scat Machine.