Whether you're out camping or just cooking out in the backyard, many barbecues use propane as a fuel source. If you have a tank with only a little propane left and yet you need the barbecue to run consistently, one way to keep the gas flowing is to connect two propane tanks together. To do that properly, you need an auto changeover regulator, which not only connects the two supply tanks together, but also empties out one tank first and then the other.
Place the propane tanks next to each other. Turn off both valves on the tanks by turning the handles clockwise.
Connect one hose from the auto changeover regulator to one tank with your hand, then repeat for the other tank. Install the threaded end of those hoses into the sides of the auto changeover valve with an open-end wrench.
Install the remaining hose from the auto changeover regulator to the bottom of the auto changeover valve using the open-end wrench. Connect the remaining hose end to the barbecue, or the other source that requires propane.
Never smoke near propane tanks, because if there's a leak or any other problem causing the propane to be exposed to the air, you could cause a fire or explosion.