Thanks Gary. The problem is that my propane tank has a 2-stage regulator on it. The first stage is on the tank itself and steps from tank pressure (150psi or so, if it's similar to bottle pressure) down to 15psi. The main gas line from the tank to the house is 15psi, and a second regulator at the house takes it down to 1/2 psi for the internal appliances.
I actually put the line and tee in already (from the 15 psi side of the 2nd regulator) and it's capped off. However, since it's supply is now 15psi instead of 130 psi (from propane bottles), I'm thinking I need a different regulator. My propane supplier requires the 2-stage system, so there's no way I can get tank pressure at the house.
Any ideas?