^ Are you sure that's all there is to it, a simple acetone wash? I know even for the powder H there are a lot of steps (erowid has a how to) and I know a lot of people that didn't want to bother with all of that.
For tar I see the main problem being the surface area. You wouldn't be able to get to the middle of the tar ball. Now I am sure it would be easier with the powdered tar, but still doubt it is just an acetone wash. I am sure it will clean it up a little, but not that much.
Yes it was Acetone, first though they froze the tar overnight in the freezer of course, then took it out and crushed it as much into a powder as they could, then they put the tar/chunky powder into Acetone, let it sit a while, and then filtered it through a funnel with a filter and refroze the tar, and might do that several times before they "wased it" to their liking,even doing some stuff to heat the tar a bit to make it darker in color..I saw this with my own eyes in Austin ,Texas, and maybe the acetone wash had an extra step, I do not really remember one, but thats been a long time, but they filtered the stuff and froze the tar first of all, frozen tar can be busted into a semi powder like form and put into the Acetone. That deals with the "big ball of tar" surface area, plus the tar these Mexicans were messing with in the first place was not the really wet and sticky tar really, it was the more hard,drier type of tar..
Speaking of Erowid, look at the pictures in there heroin section, pics of tar, notice the pics of tar taken in the US are all sticky and wet tar, while the pic of tar taken in Mexico is the hard,dry type of tar..this is a sign that higher grade tar in Mexico before it is cut with variuos things is the hard drier type, look it up for real, I saw the pics and saw how the US taken pics of tar were oozy, sticky wetish tar, and the pic of tar taken in Mexico looked more like a piece of charcoal almost..it's a trip , they are defintely doing something from Mexico and the US with the tar and cuts..check it out..