Edit: DO NOT DO THIS. You'll either not time it right, and have the toilet blow up on you, spraying you with ceramic shrapnel, or you will time it right, and blow an entire wall of toilets off the wall, destroying a fair amount of the school's plumbing.
You definitely shouldn't do this, but you can get gelatin horse pill capsules off Amazon that are over an inch long that could delay it. But don't do it.