I'm at a complete loss as to why the Sims don't use the sink in the kitchen (see pic below) only five feet away from the table they eat at but will go to the other end of the house to use the bathroom...
I heard by default the sims use the most expensive sink not the closest one. so I put the most expensive sink in the kitchen and have had mixed results. So I'm not sure if there is a real rhyme or reason to their behavior or if its just RNG.