Kurt Gavin wrote:

I've got a 500 gal tank. How do you determine how many gallons are currently
in the tank?

Thanks

Accurately - weigh it and compare to the tare weight that should
hopefully be listed on the tank data plate.

Roughly, get one of those liquid crystal stick on propane tank gauge
things and keep moving it down the side of the tank (doing the hot water
thing) until you find the LP level. You'll have to watch extra closely
since the tank wall will be thicker than the wall on a 20# tank. Just
remember that other than the half full point, the scale is not linear
due to the cylindrical shape of the tank.

Pete C.