First I thought to add a paper boat and drop a Tim Curry / Pennywise reference but then came the beach ball idea.Reminds me of the first Alien movie for some reason.
That was the task I gave to me, making a brick material showing different states of wetness.(and on the right side, the wet stone looks a bit unnatural to me)
... but that would have to be the cleanest sewer ever. Not that I'm an expert.