I've done it dozens of times,mostly on tractor and equipment tanks.It is not perfect,there is no substitute for blasting,but I have had zero problems doing it this way.I use a quart or two of Black Beauty sand,(coal slag),a gallon of muriatic acid,dump it all in,strap it up and let it turn.Sometimes an hour,sometimes ten hours.That is the simple explanation,the A tanks need a little fancier rigging.The A tank has to have the top almost perfectly 90 degrees to the wheel,if it is not the underside of the top will not get done.Also,if they are turned too fast the sand will migrate to the the other sides of the baffles and stay there.I check after a half hour and if there is still a cup or so of sand in the center I know it is swashing back and forth in there.It is not a perfect process,but the one I have that was done in 1972,just before I started driving is still holding up fine.I can still see the black spots left behind just as they were back then.But,the tank has never since been subjected to the use it had before that.Has always been under cover since,has not been filled from cans that sat in the sun making water,and for most years it has had a cup of ATF thrown in over the winter.That tank accumulated a total of 1/2-3/4 inch of powder in the bowl during all those years.I dumped about 1/4 inch out in the late 80's,because the gasket went bad and I had to take it apart.Then I did it again a couple of years ago,same reason,bad gasket.The REAL fun is getting the sand out.You will get 98% with a water hose and swishing it around,that other 2% is fun.The one I did last summer is showing a little gray powder in the bowl,with just a couple specks of black sand.I just don't see any perfect way of doing it.I have a tank bottom that was given to me by a guy that cut the top off for a hot rod.I played with it a little,and peeled one of the baffles off the bottom.There was rust between the baffle and the bottom of the tank.In theory that is not going to stop,in reality I wouldn't worry about it.With the alcoholic gas now,attracting water,who knows what will happen?