My father in laws need a water heater swapped out, when looking at the water heater, they guy who did the install has the normal hot and cold hooked into the top 3/4" copper lines. And then where those lines go into the wall (to the bathroom) there is another 1/2 in line comming out of the bathroom that hooks into the Drain on the water heater, there are two faucets on the line and two 1/4 turn ball valves in the line as well, both are turned to be 1/2 open. Any idea what the purpose of this line would be? There is no circulating pump or anything installed that we can find?