Like these guys said, the foam won't hurt anything, but if you MUST have less foam, there is a product you can find called Saniclean. It's from the same company as Starsan and is basically the same as Starsan, but a low-foaming version.
Pour a glass of hot water down the side of the tank, then run your hand down from the top along the path you poured the water. Where the tank is warm, it's empty. When it starts feeling cool, that's your propane level.