This is getting away from mirrors quite a bit, but DON'T put teflon tape on fittings that will have a fluid going thru them. It'll probably be fine the 1st time, but when you remove and re-install the fitting, threads of the tape will be pushed into the component, and can mess up metering, valves, etc. My business is refrigeration and commercial kitchen equipment, and I know that many gas appliance manufacturers will void warranties if they find evidence of teflon tape in their products. You might try teflon pipe dope for a sealer/lubricant. It works great.

Lar.