D&H designs subsurface drip irrigation systems so proper pipe flushing, including mainlines, submains, and laterals are easy to maintain. Submains are the same as a supply manifold for the dripline. In subsurface drip system design, pipe size is often determined by flushing needs. As pipe size increases, friction loss decreases which reduces pumping cost. The piping system must allow the flow rate necessary for consistent irrigation but also considerations must be made so flow rates ensure proper flushing velocities in the system. D&H realized when submains and flushing manifolds are placed below the driplines, solids will tend to collect in the submains and flushing manifolds rather than enter the driplines. D&H designs their piping systems so that friction losses in combination with elevation changes do not exceed the allowable pressure variation for the target system design uniformity.