· Crushed #2 Gravel. This primarily 1″ crushed, washed gravel with a top size of 1-1/2″ is often used for drainage around perforated pipe, under concrete slabs, and as a coarse driveway topping for soft, very muddy driveways. NYSDOT 703-2, size 2. Ideal for drainage around a perforated pipe. Clean, washed, a bit difficult to shovel.