Have seen newspaper, wrapping paper, cardboard, black plastic garbage bags, towels etc. 

And then use a plastic easy to remove cover to cover up the pipes, and then lay your floating floor on top of that?

It’s a plastic box inside a cardboard box .

I got 96 rolls of tp, 2000 plastic forks and 1000 styro plates at a scholarship auction for about $40. 

It is only about 40 minutes to Disney, but most go to Mount Dora for the old Florida enjoyment away from blatant tourism of the plastic mouse ears.  

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.