As mentioned, you will want to turn off the main valve during a power outage, which means no water will be able to come into your home. However, if you are proactive and have extra water on hand, you can manually flush the toilets by simply dumping buckets of water into them. You can either have an emergency stash of water in individual containers, or, if you know a storm is coming, you can fill up the bathtub so you have water easily accessible to flush the toilets.