Sorry for the above. I posted before I really read the article. It's really about vacuum toilets on airplanes. You want to know about the green chunks of frozen stuff that fall to earth in urban legends, right?

Think RV. They have holding tanks that contain waste matter until ground crews drain them. Likewise, they have potable and non-potable tanks of water. You should not drink from the faucet in the restroom. Other faucets are questionable, as one recent survey found up to 20% of all potable water sources on planes were found to have some strain or other of e-coli bacteria (not necessarily harmful unless you have a weak immune system).

Then again, I'm certainly not an expert. Others have written on the subject in this forum. Might try searching.