I used to have a 1968 pick up camper that didn't have a grey water tank, did (it was just the sink, no shower). Camping world or somebody was selling one of those collapsible 5 gallon water jugs with a lid that had a threaded fitting for a garden hose.I hooked up one end of a short garden hose to the grey water fitting on the camper, and the other end to the fitting on the water jug, the packaging stated that it met requirements for gray water storage. Of course it only held 5 gallons, but I used it in Olympic National Park without any problems.