I don't know what current rules and regs are but when I had a popup back in the 90's, I hooked up a garden hose and routed it so it wouldn't drain into anyone else's site. Only thing I had was a sink. Never had a problem and seemed to be a normal procedure at the time. But I also know a lot of discharge laws and regs have changed significantly since that time. Nowadays I think I would have some kind of container.