It's not hard to pull the tank. That's what I'd do, but if you dont feel comfy doing that I know for a fact that if you take the under cab filter off it'll squirt gas all over your arm until the tank is empty down to the filter. Have a safe collection pot to put it in and keep away from sparks!
If you pull the tank and dump it, you can just dump it IN A GOVERNMENT APPROVED CONTAINER (i use the government supplied grass in my back yard
) and wash it out with acetone. If it got gummy though, you might need to let the acetone sit in it for a long, long time. And you'll probably need to replace the lines too.