People are now voluntarily covering their drains at home, wearing gloves, safety glasses, masks and plastic suits walking outside, touching elevator buttons and door knobs with metal prods, followed by immediate torching of the contact points.

So yes, it is likely that it was mold or mildew, and it is likely that it has stained the plastic & rubber in such a way that you will not get the stain off.

Use a fresh new previously plastic-wrapped roll of the premium 3M blue tape for this, or use new green Frog Tape sealed in its package.

It stretches 350 miles across the state heading to Marcus Hook just outside Philly where the materials will be put on ships bound for Scotland to be made into plastic.

The more modern plastic drains can probably take whatever you can put down em, but the older metal ones (and the metal under sink parts) can corrode / start leaking. 

Just replaced these SOR Lowes.White doors are steel $100 eachBurgundy is solid Oak $180 already coated with a plasticized coating.Took my maintenance guy 2 hours per door including completely removing the old doors & all new trim & caulking.I also get Appliances catch & dent.  

If it's a Romex type plastic sheathed wire, I wouldn't do the whole house.

The plastic barbed ell that screws into the pitless adaptor has cracked at the threads .  

My parents 1917 house had Clay and roots, and they had to pay to have a plastic liner put in. 

We switched over to plastic wine glasses.