I use one of these two methods:
1. high powered plungers
2. Draino Crystals. Fill the grey water tank 3/4 full. Follow the instructions on the Drano can/bottle. When you flush the drain so the Draino goes into the holding tank, fill the holding tank to full and drain the tank.
Usually the plunger works. However, with three females onboard, the Draino is needed several time a year. To date no problems with the tank valve seals.
2005 Newmar KSDP 3910 + GMC ENVOY XUV 37K lbs Moving Down The Road
The Avatar Is Many Times Around The USA
Nobody Knows Your Coach Like Somebody Who Owns One Just Like Yours