[retiredchuck]

This is what I do and it works all the time.After I dump the black tank,I close the black tank valve and with the hose hooked up to the backflush I refill the black tank. I go to the readout and you might have two or three lights on,just keep on filling the tank on till the last light lites up and you are full.Shut the water off and open the valve.Most of the time it will cleare all the lights except for the one that states that is empty.if not do it again.the most I have done it is twice.Then I let go of the gray tank,after closing the black tank valve.The force of the tank draining after Its been refilled helps to clean the sensors. Try it .....You have to be by your sensor readout so you dont overfill your tank and have a flood in your trailer.Remember you have the vavle close to refill your tank.