RE: Draining fuel and running the engine until it quits
It shouldn't affect the cost. I'm not going to discard any un-used fuel, just keep it in the tank of the airplane between flights.
What I am saying is I'm not going to contaminate the new $20 plus dollar a gallon fuel with the gunk from the muffler anymore, just as a precautionary measure.
It's just not worth taking the chance in my opinion.