When all the toilets in the house are in use, you may not pee in the sink. Seriously, my five year old daughter did this once. She used the sink when her brother was using the toilet. I heard her brother laughing hysterically and I walked in on the scene. Her legs were hanging off the sink and she was asking for toilet paper.
I am the Meanest Mommy in the Whole Wide World. I am forced to make rules & observations that I never knew would be necessary before I became a parent.
Rules by the Meanest Mommy in the Whole Wide World 
When all the toilets in the house are in use, you may not pee in the sink. Seriously, my five year old daughter did this once. She used the sink when her brother was using the toilet. I heard her brother laughing hysterically and I walked in on the scene. Her legs were hanging off the sink and she was asking for toilet paper.