Why is my toilet bowl black?!

Check the inside the toilet tank. It may be growing mold in it. If it looks dirty use bleach to clean it. Being the toilet is the basement it could be water backup when the upper toilets are being used.

my basement toilet would get black and scuzzie from mold. Gave it a good glug of cleaning vinegar covered it with plastic wrap and let it sit for24hours.

Pour white vinegar in the tank and toilet and allow to sit overnight.

Maybe it is just stained from sitting unused with some antifreeze chemical

i would use the vinger.

Thanks everyone

• Could be it was cleaned with a soap pad. This happened to me. I cleaned my back toilet with a Mr. Clean Miracle Eraser and some Ajax (powdered).
• I tried vinegar, tried Bleach. They didn't work.

Hope this works for you.