I recently acquired a vehicle that has had the same fuel sitting in it for 10 months at about 1/2 tank. It took it in for a GA emissions test and the tech mentioned a bad smell (stale gas I presume). It passed the emission test (gas cap ok and computer test). He recommended draining the tank and filling it with premium fuel for the next couple tanks. The vehicle runs fine. Do I really need to drain the tank vs just filling it (and maybe use some kind of additive like Techron Concentrate, Royal Purple Max-Clean Fuel System Cleaner and Stabilizer, Startron or something else etc ?