We had a tankless water heater installed about 1 1/2 years ago. It takes probably 2 gallons or more of cold water going down the drain before we get hot water anywhere in the house (bathroom sink, kitchen, shower etc).
I have seen Richard installing something under a bathroom sink that 'bypasses?' the cold water back into the cold water pipe which lets the warm water come through almost instantly. To engage this action the person had to push an electrical(?) button which was installed on the side of the cabinet.
I would like to show this to a plumber, but cannot find the video on this website. Can somebody provide a link?