I haven't been on the forum for a while and I have been bad and haven't taken care of my RV for about as long. My wife and I haven't used it for about 5 years and I use to go out and start it every ot...
Check out NAPA or auto parts store - They have gas additives you can add to the tank - It would be hard for me to drain a full tank of gas haha...
Bad gas usually means water has been mixed in with it. I forget which way it goes but if they are left setting one will eventually separate rise to the top of the tank... Using a hand pumper you might able to siphon out the bad stuff... This could be a dangerous thing to play with however...