lines off the toilet-tank at the meeting
saunters casually into the Handicapped head with the lockable door and the big sort of crib built around the shitter itself for crippled lowering onto the toilet and does like maybe two, maybe three generous lines of Bing off the top of the toilet-tank and wipes the tank-top off both before and after with wet paper towels
Context
The using happens inside the recovery machinery itself: Lenz slips into the one lockable head at the Brookline Young People's meeting during the raffle-break, does his lines off the toilet-tank, and reassembles the collection-plate dollar he rolled them with so that all evidence is erased. The meeting is not a refuge from the drug but the drug's most convenient cover — the one place with a locked door, a scheduled break, and a crowd too pious to suspect.