black stuff in toilet bowl-long

[IrishAyes]

7. You should keep the lid down always for more important reasons than cats.

When the toilet is flushed after normal use, the air that shoots up carries with it a slew of bacteria and fecal matter that you can't see. This cloud can spread as far as 5-6 feet from the bowl and contaminate everything around.

You did such a great job of cleaning that if weekly additions of a cup of vinegar or bleach to the tank don't stop the black stuff from reappearing, you might need a plumber to check your water lines because no telling where that gunk's coming from. Try this: draw water in a clear glass or bottle from the kitchen faucet at night, let it sit on the counter overnight, then see if it's clear in the morning. That would give you some idea of how far the problem extends. You might get "lucky" enough that you only need to replace some of the pipes closer to the toilet.