The stopper included with the Single Bowl RV Bathroom Sink # 37295351 is made of a rubber material that will allow it to sit slightly above the drain until you push it down into the drain to block it. When I tested it in the warehouse it had roughly an 1/8" gap when just loosely sitting in the drain. In my opinion this stopper is more so just a drain plug that you'd want to insert when trying to completely block the drain. view full answer...