How to recirculate a 4 bucket waterfarm system with a res and controller?

[The White Snoop]

You can use your resivour as your controller and just keep it level w/ the buckets,just do as latewood said and use a pump to empty out the system. You can also switch the feed pump(at nute change time) to your empty out drain line

BTW. Shut off valves are lifesavers in the long run. I would run one at the begining of the drain line and one at the end of your empty out drain line.