Cleaning a filler neck

I did a crankshaft with 1 gallon of Evaporust...I opened a black trashbag and layed it in my kids sandbox. I pushed the crank into the bag/sand until it was below the sand line, then you backfill the voids with sand so the trashbag is now formed to the crankshaft shape. make a berm with the bag then you pour in the Evaporust. With some luck, you can completely cover the crankshaft with 1 gallon of evaporust. Let it soak overnight and take it out. I toweled it off and let it dry in the sun. No more patina. Sucked the evaporust back into the container, only lost about a cup.