muriatic acid is powerful stuff, I dont know i'd suggest shaking the gas tank while it's full of the acid. do the handful of washers bit with water or vinegar, then drain and then do the acid and just let it sit for an hour. half and half acid and water mix should be more than strong enough to eat away any rust. You should also be wearing goggles and a respirator (not a dust mask) whenever you're using the acid. to nuetralize spills, use baking soda, then rinse with water once the fizzing stops, don't just swish it away, that shit is poison and you're just washing poison into the ground if you hose a spill off. If you want to nuetralize a whole bucket of waste you're going to need like two of the big boxes of baking soda, and a bucket that's more than twice the volume of the waste, cause it bubbles a lot when it neutralizes. It's way more dangerous, but you can neutralize it easier by putting your respirator gear back on, taking the bucket out to an empty parking lot, and pouring a bottle of ammonia into it. THIS CREATES CHLORINE GAS, WHICH CAN KILL YOU SO DON'T SCREW AROUND IF YOU USE AMMONIA.