Grey tank stopped up won't drain

Lotion rich body soaps will build up along with hair and cause clogs. We have used "septic safe" drain cleaners when we had slow drains and the plumbing in our rig is the same as a house. We do make sure there is some water in the grey tank to start with and then after running the hot water in the drain as instructed, we do a dump. Only had that black tank refuse to drain 1 time and learned to use plenty of water when flushing after that. It was a toilet paper jam up. Didn't use enough water for the tp to break down. We also always leave the valves closed until the tanks are full and usually have to do 2 grey in between doing the black. It's not good to dump when the tanks don'g really have much in them. You don't get the water pressure from in the tank to push things out. We are full-timers also and other than the problem in the 1st year 7 yrs ago - no problem since.