In this video Gary Bunzer tells us how to tell the fuel level in your RV propane tank. If you don't have a flow gauge to tell you the level in your tank, it will be more difficult to tell how much you have left inside. Try looking on the tank itself to see if there is a gauge on it that is monitoring how much is inside. You can also tell by throwing warm liquid on top of the tank to see where the condensation is collecting at. As soon as you do this you will have an idea of how much is left in your tank.