Fills propane tanks but not by pound nor gallon. They will only "top off" an RV tank. They won't top off any other portable tank. So, I wanted to buy their empty new 40 pound tank for my tank top dual head radiant heater. So, sometimes, I might only need 2/3 fill to get through a work day. They say they will give it a 2/3 fill but they will always charge me for a full tank quantity of propane. So, they can top off a tank but charge for a full fill unless your tank is permanently connected to an RV. Doesn't make good business sense to me. They have 40 and 100 pound portable tanks for sale but who would buy them knowing you will always have to pay for a full fill each time you only need a partial fill (as when cold winter temps diminish tank vapor pressure requiring you to keep the tank half full or better).