Good point on the bottles!
I always point this out to people with gas grills. If a 20# propane cylinder costs $20 to exchange, and they only fill them about 80% full, you're paying roughly $6 per gallon for propane. If you already have propane at your house, you could run a line from your bulk tank, get your gas for 1/4 the price and never have to worry about running the 20# cylinder empty. If you have natural gas at your house, even better, because it's about 40% cheaper still.
The downside? Don't forget and leave your grill on! A grill will burn through about 1/2 gallon of propane an hour...if you multiply that by say...a week...it could be sort of expensive.
Sorry to highjack the thread. Back to the original question...1/2" should be fine.
Phil