My experience has always been (at the expense of others) that you will only be able to aggitate what is in the center of the tank. The normal problem areas are
behind the baffles on the top, --and the sides of the baffles themselves. Look at these pictures and visualize just how difficult it is to get aggragate in thru the cracks between the tank walls and the baffles (--and out again)
PLUS get it to scrape the areas you are wanting to de-rust.
Honestly, I get many tanks in here that have been "spun & sealed" and as you can see in the pictures, the rust continues and soon thereafter the sealer turns loose and the problem resurfaces. Also note the green fish aquarium rocks that were used during a restorers tank spins, --and then "left behind" when he couldn't get them out. It is also worth noting that even though they were used, it never really de-rusted what the owner had intended, --or thought he had accomplished!
I could also fill this page with pictures of nicely painted gas tanks off of restored automobiles that are loaded with sediment. My suggestion when you find a tank is that bad, is to find an alternate method or tank.
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