The theory of how to clean the inside of a tank could fill a whole book!These are the threads. Probably you all are quite used to do these things with perfect results, but my performance doing threads up to now was rather miserable...www.antiquetractorsforum.com
Couple of people said they sloshed some sand and gravel around inside to clean the tank before pouring that tank lining stuff in; bit it seems like a bodge hoped you had a better way to do it properly?
These are the procedures I have done so far in several different tanks:
First thing to do is to take a look inside the tank checking the amount of dirt, rust, pitting, foreign objects, holes, etc. Take your time and use a flashlight; fiberscopes are also useful and they are not expensive nowadays. Do not forget to check whether the filler neck has a rim inside the tank, because if it has one it will be quite difficult to take out completely whatever you use to clean it if it is a loose matter like sand. Clean the inside with water and some sort of strong cleaner for oily/greasy stuff. Best advisor for the stuff to use is your own wife. This will clean and dissolve most fuel remnnants which might creat fumes. Rinse it several times. If the bottom is seriously pitted, forget about cleaning it and go to a welders to replace the whole bottom and bumps if there is any. That happened to my MF65. If there is dirt and light rust with no pitting then I put a piece of chain about 2 cm wide and half a meter long inside and another piece of a thinner chain that can reach all the angles of the tank, pour some generous amount of rust solvent of your choice (not too flammable, please) and then you can play the fool shaking it for hours or tie it to a rear rim of a jacked up tractor, start it up, engage the first gear and go for a beer with tapas while it cleans. Check the progress between beers until the inside looks pretty, remove the chains, drain the solvent, rinse with water and whatever your wife tells you, let it dry thoroughly and once you are satisfied, pour some fuel or engine oil and shake it in a sportly manner and then go to celebrate it with with another beer. If the tank shows strong corrosion but you are convinced that the metal thickness is strong enough, once you have cleaned the inside, consider to use a gas tank sealer. But if you see the sheet metal weakened or even holed, the welders is your only option.
This what I actually do, but, remember, I am not a pro, just a shadow tree mechanic…