I find flushing them at the end of a grow with just slightly soapy water works well. I use a 30ml syringe. I don't flush again with clear water as I use minimal soap. I can flush a 4 pot system in less than 5 minutes. When I flush I leave the tubing connected to the valve so that both get flushed together. I flush the feedline from the res with it detached from the system. I later simply made up a spare tubing array to just swap out at the end of a grow. Then when cleaning trays and valves, i flush the removed tubing array.
