Adjustable toilet flappers are similar in shape to universal ones. What's adjustable is not the actual shape of the flapper itself, but rather how much water it dispenses with each flush.

The universal Super Flapper™ is uniquely designed to convert into two sizes so it can replace either a 2-inch or 3-inch toilet flapper. Adjustable Water Usage ...

If you have recently replaced the tank flapper and your toilet is still running, it may be time to pull out the big guns and replace your ball cock, aka fill valve.

Number of tools needed: 3 (adjustable wrench, putty knife, wax ring) Running: If your toilet constantly runs, it’s probably the flapper in the tank. This is so easy you don’t even need tools: ...