In some homes, drains slowly accrete a buildup of soap scum and other gunk on the insides of the drain pipes, which slows down the rate at which water goes down the drain.
This is generally treated with a "slow drain opener," a mix of enzymes and bacteria. Treatment is typically done once a month.
This idea is for a continuous release version of those enzymes and bacteria, using a tablet that is dropped into the toilet tank.
Tablets would would still need to be added on a monthly basis... but if it includes a dye (green, perhaps), it would be very easy to see when it needs to be replaced.-- goldbb, May 24 2010random, halfbakery