I live in Northern Nevada and I am installing a sprinkler system. My problem comes from owning an older house that was put on a slab. I know that I have to place the (Stop & Waste) valve at least 18" underground to keep it from freezing but my water supply comes from a pipe that is above ground. Because the pipes are all in the cement slab, I cannot get to them and have to tap into the supply that runs to the outside of the house. Do I still need to have a (Stop & Waste) valve of should I connect the valve where the supply exits the house and then install an additional valve to drain the system between the supply and manifold so that the water does not freeze in the winter and damage the valves, pipes and manifolds.