Shut off the valve on the small tank you currently use beneath or beside the grill, turning the knob on top clockwise to halt the gas flow. Also close the main house tank valve. The control knob is on the top or at one end of the tank.
Disconnect and remove the regulator from the small tank and your grill with pliers. You will not need that part because the house propane supply has its own regulator.
Measure the distance between the home propane supply and the grill. This measurement is the length of gas line needed. Purchase a gas line from a propane dealer or hardware store. The propane gas line needs to have a coupler on each end.
Hook the gas line to the regulator on the main propane tank, tightening the connection with the pliers. The main propane tank is typically behind a house. Run the line below or alongside the house deck or patio to the grill. Don't run the line across the ground where it could be cut by a lawnmower or garden tools.
Attach the connector on the other end of the gas line to the gas nozzle on the back of your grill.
Open the valve on the main propane tank, and check along the line to the grill for evidence of a leak. Propane makes a soft, hissing noise and carries a distinctive odor. If you notice those signs or other signs of a leak, shut off the tank and reconnect each end of the gas line.