Waste doesn't seem to be flushing from holding tank

Fill the tank with water and let it soak then drain, I would not use draino or other drain cleaning products not good for anybody. The water should be enough then if you can get the clear adapter with the garden hose adpter and drain off a little at a time till it drains. Our camper sits and the tank is open all the time. I have an adapet on the tank washer that can be turned on and wash the tank out every couple of days when we are there.