Is the public gas company allowed to remove and resell remaining propane from my tank?
The delivered fuels–propane and fuel oil–are not regulated. The lease or rental terms of the tank probably dictate charges of services such as emptying the tank. Other propane vendors will not touch the tank if it is not your property. In the future, if you live where propane will be one of the fuels used, it may be well worth the investment to purchase a tank (rather than rent one), because it provides you the freedom to purchase and dispose of fuel as you see fit.