In a tight space, you need modern solutions to maximize flexibility. The SinkPositive GreenFlow Toilet Tank Sink is the perfect space-saving solution for small bathrooms, tiny homes, RVs, and the eco-conscious. This sink replaces your toilet tank cover and uses the tank's refilling operation to pump fresh water to the sink faucet - draining the used water into the toilet tank for flushing. Our lifetime warranty guarantees the durability of this sink for as long as you own it.