I have a drum of a 6-1 water/molasses mix sitting outside my shop... works great for derusting everything from wheels to heads to blocks and everything in between.

A 40lb bag of dry molasses (animal feed) is about $18.00.... I mix a fresh batch every spring. 40 bs. lasts me three years.

I use my shop crane to lift heavy parts in and out of the drum. When the cold weather comes I simply dump the old stuff out into my driveway and wash it into the street... it's all natural so the greenies can't say a thing.