Another story of the same type was somebody trying to recover waste heat from shower drain water to put back into the shower water. It was poo-pooed for violati

Another story of the same type was somebody trying to recover waste heat from shower drain water to put back into the shower water. It was poo-pooed for violating the 2nd law or something. But the poo-pooer neglected the fact that hot shower water is made from a mixture of hot and cold water, so the cold water could be heated by the warm waste water.