Unlike the Flo N Gro, this DIY I did uses gravity to help it along. In its purest essence, there are flood fittings (see below) that can be set for a minimum level and maximum level of nutrients. A pump in the reservoir, set to a timer, floods for 5 minutes at periodic intervals. 5 minutes is enough time for the roots in all plant sites to get a good soaking before it drains again. The pump runs for the entire 5 minutes, but the overflow fitting keeps it from well, overflowing.
Here's a little more detail with pics on the DIY hydro system I built:
The grey "Brute" rubbermaid garbage container in the lower right of the pic is the reservoir. Notice on the lid there are 2 hoses, and an opening for electrical. One hose is "flood/drain" connection, that connects to a 200 gph pump inside (controlled by a timer). The other hose is for the "overflow drain" and simply dumps the water back into the container after (and during) a flood when it rises to a preset level. Finally, there is a small blue airline that runs paralell to the power cord for the pump, and serves to aerate the reservoir (connected to a small, un-pictured airpump). When the system floods, the pump in the reservoir pumps the nutrients from underneath the far right plantsite (top right of the photo). Along the front of the containers is tubing that connects the plant sites so that during a flood, all 3 plant sites are flooded, too:
The far-right plantsite is the controller for the other plant sites, too. Inside are botanicare flood/drain fittings (available at most hydroponic stores). One of the fittings is for flooding and draining, and one is for overflow. When the system floods, it comes through one lower fitting, and will continue to flood until it reaches a level set by risers in the other fitting. While the system will flood as long as the timer runs, this second fitting is what keeps you from overflowing. I have it set to a height so that the netpots are thoroughly drenched, but not so high that it overflows. You can buy the fittings in a kit like this (google or check your hydro store). Notice that there are 2 different heights. The shorter one is for flooding and ultimately draining (once the flood cycle ends, the nutrients will drain back through the pump to the reservoir). The second, taller one has risers that allow you to set a max height for your flood before it simply drains back to the reservoir. Here's what I used for fittings (by botanicare):
This is a picture from when I was building it. The lower fitting now has one riser piece to allow for a set level of nutrients to stay in each plant site vs. a full drain. THe top piece on these are a filter. So, they drain at the bottom of that piece. In this earlier picture, the lower fitting would drain flush to the bottom (completely). The overflow fitting has (3) of these "risers" and allows for the nutrient level to flood the entire bottom portion of the netpots. The fittings are easily installed by cutting a (I believe 1 1/2 inch hole) and then screwing them together top and bottom:
In this photo of the far-right plantsite/controller, you can see the overflow fitting that sets flood height. Unpictured is the lower drain/flood fitting, which isn't visible due to the front of the container. Notice I'm starting to just starting to get roots showing through the bottom of the netpot. The floods should allow root development all along the netpot sides, while dwc only typically results in a mat of roots extending mostly from the bottom only.
I tried to get a pic of the shorter flood fitting in the container, which can be seen to the right of the visible root in this photo. Normally, it would be fairly flush to the bottom, but I've installed a riser (available individually at my hydro store) so that after a flood, a pre-determined amount of nutrients are left in each plant site, which are aerated to perform in a DWC manner. When not flooded, the nutrients are about an inch, inch and a half below the netpots - fairly ideal for recirculated DWC I think. Without the extra riser and aeration, this would be essentially be a gravity assisted Flood/Drain unit. The riser and aeration in the plant sites allows it to be DWC when it's not flooding.
Here's one of the other plantsites. The nutrient level is controlled for it by the far right "controller" plant site, so aside from being connected in the front, they really just house the plants and contain an airstone (well, bubble bar or whatever you call this thing that acts like an airstone):
Really hope this helps -- let me know if I missed anything or if you have more questions!
