Put a bucket in your shower to collect the water used to get hot water to the shower and the water you use while showering. If you take long showers you may need 2 buckets. Use this water to flush the toilet by pouring the water directly into the toilet bowl. You can also collect the water from the sink by placing a pan in the sink and pouring it into you flush bucket. It is a lot cheaper than a gray water reuse system and you get a work out lifting the buckets.