A 100-lb. propane gas tank holds approximately 24 gallons of liquid propane when fully fueled, or nearly five times as much gas as a standard 5-gallon bottle typically used with a gas grill. The main advantage of a 100-lb. tank is convenience, since you can grill much longer between fuel refills. One trade-off is the added up-front cost of filling the cylinder with propane. The propane tank connects to the grill in the same manner as a smaller tank, although you may need to purchase a longer regulator hose to reach the valve connection.
Measure the distance from the valve on the side of the 100-lb. tank to the connectors on the rear control panel of your grill, using a tape measure. Compare that distance with the length of your current regulator and hose to determine if a longer regulator is needed. Hardware stores and specialty grill shops carry gas grill regulators.
Twist the valve knob on the top of the propane tank clockwise to ensure it is closed.
Attach the larger coupler on one end of the regulator hose to the valve on the top side of the 100-lb. tank, turning clockwise to secure.
Connect the hose (or hoses, if you have a two-burner grill) to the valve control stems on the back panel of your grill. These connect almost the same way as a garden hose to a faucet, but twist clockwise to attach.
Turn on the gas at the main valve on the tank and listen for any sounds of leaking. If you hear or smell any propane escaping from the connections, shut off the main valve and reconnect the regulator at all points before attempting to use the grill.