Now you're on to using less soap, and wasting less plastic!
Behind the scenes: Soap itself doesn't really clean your hands. Soap merely makes most dirt more happy to mix with water than it is to stick to your hands. Hence why this product is so great. You can start with the foam (already 4:1 mixed with water) and do most of the hand cleaning with that, then simply use a LITTLE tap water to rinse off. Water savings too!
Downside - its more work. Alternately, you could prepare some watered-down hand-soap in a spare 4L jug, and keep that handy to refill your pumps.