Guests overflow bathroom with poo water

I had some really nice guests staying in my downstairs room and everything was completely fine until I went to do the post stay cleaning and found that my guests had used the toilet brush to clean up their poo and didn’t wash it.  The brush holder was filled with poo liquid!  I noticed earlier that they took out the bathroom mat before they left and I asked them curiously why it was there.  They gave me a nervous laughter and now I know why. Not a big deal.  I’m not poo phobic or anything.  Just wish they told me.  I’m sure it was already embarrassing for them.