How to clean pistons

He's prolly refering to 3M scoth-brite pads. Should be able to get them an auto parts store,a hardware store or a store that carries auto body supplies. I believe theres 2 different colors Red- For general purpose/moderate cleaning and Gray for less aggresive situations (such scuffing paint or primer or interior pieces/chrome). I'd go with the grays first and if they aren't cutting it then go to the reds.
 
You could also use a razor blade to get the big stuff off the top of the piston, just care not to scratch it. If there is carbon in the ring lands, you can take an old ring and break a 3-4 inch piece off and use the non-broken end of it to scrape inside there.