"No Fluorescein Dye Markers down the toilets please"
As an aside, I had an eye problem a few years ago and part of the diagnostic process involved me being pumped full of fluorescein dye and photographs taken of my eye to see if a blood vessel was leaking. Back at home and I went to a quiz night at the local golf club. The dye had to go somewhere, and I went to the urinal in the golf club which was one of those long white porcelain group troughs. Imagine the looks I got for the rest of the night as the stream of very bright thick yellow fluid slowly made its way down to the drain at the other end of the urinal!