If you use pump soap dispensers for hand washing, wrap a rubber band on the lower half of the pump.  Then, when you and the kids press the plunger, it will only go part way down.  Resist the urge to “double pump”.  An amount about the size of a dime will do the job really well, and you’ll use ½ as much soap in each bath and the kitchen.  Put $5.00 in the tin.