At long last, we have two functioning bathrooms again. Yeah!!
Middle Son was using the restored hallway bathroom. After a while, I decided that I should go and check on him. I found that he had taken off all his clothes and dumped half a bottle of shampoo over his head.
I believe that is the 4th time in the last two weeks that I've found him with half a bottle of shampoo on his head.
Thus, we have a new house rule. ALL shampoo, conditioners, etc. must be locked up when not in use.