Originally Posted by ALANSD
Its the line that screwed into the furnace line. Guess i can try 3/8 and 1/2 and see what fits
LP lines are typically connected using flare fittings. They make plugs and caps for male and female connections.
I'd think the fitting size would be 3/8" but a PO may have changed things up. Snap a picture of the disconnected fitting then head to the hardware store. A photo will help you, or the hardware guy with the selection process. Most of the "Box" hardware stores carry these.
As for leak detection, some soapy water applied with a spray bottle will usually ferret out any leaks. Of course an open flame works too, but I'd go with the soapy water spray.