It would be cool if toilets, sinks, and bathtubs could get clogged, requiring you to use a plunger to clear them. Then the plunger would finally have a purpose in the game and it would add a bit more realism.
However, having an option to turn the feature off would also be great for players who aren't into it.

Here’s how it could work: Let’s take the toilet as an example. You’d use it normally, and then completely at random it would get clogged. You’d receive a notification alerting you to the blockage. It would also be cool to have the choice of either finding the toilet yourself or having a small marker indicate its location.