As you probably know, one of the rules of graf is that all paint has to be stolen, or "racked" (from the display racks they keep spray paint in). Paint is usually locked up these days because we stole so much of it, and now in NYC its illegal to sell spray paint to anyone under 18 or 21 or something.
The usual technique was: everyone had a big baggy black M-65 army jacket. This jacket has a waist drawstring. Tie that up tight, zip up about 3/4 of the way, fill upper portion with cans of paint, 12 cans will fit pretty easy. There is also a drawstring at the bottom for the really ambitious. Some stores you could just fill a duffel bag.
Go to the grocery store and steal the caps off a bunch of cans of Easy-Off oven cleaner. These were the original "fat caps" that make the paint go much wider than the standard "skinny caps" that come in the can (keep those too, for outlines and details). Fat caps are the key to throwups, and essential even for many letter styles. Nowadays you can buy all sorts of fancy special graffiti fat caps; we did not have that shit.
Of course, you can't pay to get in the system. So you have a bunch of kids, B-Boys, longhairs, and punks, of mixed races (always a sign of trouble), dressed all in black (not at all common then), jumping the turnstiles with duffel bags of paint, at the last station on a train line (where they lay up trains overnight), so cops get called right away, and you have to move fast.
Walk off the end of the platform into the tunnel. Turn your black army jacket inside out, so the overspray goes on the inside so you don't get grabbed on the way home. Work gloves, same reason, and the system is very very dirty. Run down tunnel to the place where there is a stairway down to lower levels, go down to the giant lay-up. Get set up, paint lined up on the third rail wood cover, get bombing.
MTA workers ("work bums") come, chase them away, or hide depending on numbers. Cops come, hide under trains or in conductor booths (all trains have the same keys, all writers have them), or if there isn't time to hide, run like fuck down the tunnel to where it comes out of the ground, climb down, hide in someone's yard.
Go out the next day to see your shit run, and take pictures, and hang with other writers. Smoke as much weed as possible, and do a little "illy" (angel dust/PCP) and acid from time to time; drink a shitload of cheap beer. Have enemies; cross them out, toy them (write "TOY" over their name, a grave insult), and go over their shit.
A whole lost world, killed when Mayor Koch put attack dogs and barbed wire fences on the yards, stopped laying trains up in the places we bombed and putting them all in the yards overnight, and began "the buff"- special acid-washing train car washes that meant you would never see your shit running, because they would only run clean cars. And lots of arrests by the "Vandal Squad", though they never really got anyone major.