(1/2) hey flatty, if you are interested in a grow setup similar to woodmans', that is called a recirculating deep-water culture, or RDWC for short. you asked about how you get the water to return to the rez since they are the same height. the answer is there are two rez's basically -- one is a true reservoir, and the other is a 'control bucket'. with the control bucket, you control the liquid height in all the buckets. the water is typically pumped from the control bucket into the other buckets, and then gravity drains the buckets back to the control bucket. as the plants drink water, that control bucket circulates and empties. when the water level falls past a certain point in the control bucket, a valve opens that drains liquid in from the true reservoir, which typically sits above the control bucket.