Matthew finds using the tub in unsanctioned ways to be rather irresistable. He's our child that has flooded the bathroom floor not once but twice (luckily for him only the first one caused water damage). Lately he's been going through a phase where things magically end up in the tub whenever Matthew needs to go to the bathroom. He insists this is a coincidence, but bits of toilet paper, hairbrushes, copious quantities of toothpaste and nearly a full bottle of shampoo all found their way into the tub. This was less annoying than the time(s) he shoved an entire bar of soap down the sink drain.
Brendan eventually started insisting on a "bathroom door must be open" policy and even insisted on adult accompagniment for a few days. Eventually Matthew got bored and mostly moved on.