"DRAIN" runs all the way around the house for draining water, but the "DRAIN" itself never moves. This is a trick question and i hope that i have given you the correct answer. The drainage system of any house covers all four sides of the house. This drinage sytem is used for draining rain waters and any other excess water that needs to be cleared from the house. The drains are connected with the roofs for draining out excess rain waters and also the water that falls out of the overhead water tanks.
