Abstract: A mobile tank mounted on a set of wheels is hitchable to the back of a vehicle for transport between a camping area and a remote sewage area. A plurality of cleaning nozzles, interconnected by a conduit, are disposed along the top of the tank. The nozzles extend through apertures in the tank wall to the inside of the tank with sets of nozzle orifices oriented adjacent the inner wall surface. Sewage is removed on-site from each of a plurality of campers or other sewage sources at the camping area and transferred into the tank. The tank is then transported to the remote sewage disposal area for emptying. The inside of the tank is cleaned by supplying water under pressure to the conduit. Water from the nozzle orifices is sprayed against the inner wall surface of the tank. The spray tends to cut into solid sewage caked on the inner wall, and a downwardly flowing film of water established on the inner wall surface washes the sewage out a tank outlet.