black stuff in toilet bowl-long

[X_Digger]

2. You might want to replace the flapper seat and gasket. They frequently break down into black goo..

The gasket between the bowl and tank is often made of a black spongy material, topped with a black rubber ring on the tank side that the flapper seats against.

That part breaks down eventually from chlorine in the water supply (supposedly- I think it's a conspiracy to make you buy new stuff, lol.)

It's a 30 minute job to replace the gasket, if you have the room to get to the tank bolts.

The other piece that is of a similar material are the rubber washers that hold the tank to the bowl.

Once it's drained and dry, try rubbing them with a paper towel- if you get black gunk, you've found your culprit.

eta: I got sniped! What he said ^ !