DIY Undercurrent DWC System (pics)

 
Ah yes, sturdy buckets and CLEAN holes are required.  I recommend finishing the holes your drill nicely.  Remove any flash from the drilling process, and ensure they're sized correctly, and use a little soapy water to assemble them.   Using a lube will reduce the amount of force needed to assemble the parts, and limit the amount of stress put on the thin bucket edges.  
 
If you rush this, or move it a lot, they can develop leaks.  

 

 
I know it's been a while, but the master/controller bucket is pretty simple.   It can be any bucket in the system, but I choose to use one in the center, on one end.  The pump will draw water out of the opposite end of the system (via the end buckets) and push the water into the master bucket.  I also aerate this bucket heavily, and use a float valve connected to my RODI system for automatic top offs.
 
Let me know if you need any specific details.

 

 
In my RDWC system, I always run my pump outside of the reservoir (Danner MagDrive)  The heat from the pump is still transfered from the pump to the nutrients.  If you run a system like this, be prepared to keep your nutrients cool, period.   

 

 
I don't mind building/changing systems, What I want is to grow the best weed with the least amount of effort during the process.   I've grown using just about every method you can think of, and probably several you never would.  The only thing I've learned is that if you know the basic concepts of hydro, you can be successful with any system.  Environmental factors, energy consumption, required maintenance, power outages, these are some examples of the variables that should be considered when choosing which way works best for you.  
 
An example of my laziness...  If I spend 1 hour a day with my plants, I'd rather that hour be spent drinking coffee, admiring their progress, being impressed by huge white root systems, moving clones to veg and veg plants to flower, etc.   I don't want to be scrubbing buckets (reminds me of doing dishes), siphoning nutrients, etc.  So I always find ways to be a more lazy grower.  I have a fish tank pump on a flexible hose that I use to drain buckets rather than siphon them.... I love that!   As I kept growing, I ended up adding a drain system to all my reservoirs with ball valves and a single pump.  Now I can drain and fill my reservoirs without extra pumps or hoses... twist a knob, turn on a pump, and done... I work hard to design my grows in a way that I can be a lazy caretaker.   I love my plants, and I love love love to grow!   

 

Hi Plucky,
 
Those are great questions.   I'll try to answer them the best I can.
 
1) I chose 3.5 gallon buckets because the physical size fit in the grow tent I put them in at the time.  Height was a restriction (as it was a DR90 II, meaning it's a split level so the flowering section was a bit short).  This would allow me to fit 4 buckets and a controller in the tent comfortable.  It was strictly size.
 
Keep in mind that the larger the buckets, the more powerful water pump you need.  The more volume of water in the system, the more air pump power you need.   You should have about 1-2 watts per gallon of air pump power.   Water pump - I don't think you can go big enough.
 
2) I've noticed that roots form the most where the path of bubbles are.  More important than a larger bucket is more bubbles.  The key to this system is available oxygen.  The more flow, the more bubbles, and the fine control over temps will maximize oxygen at the root zone.  S o try to use at least 2 watts per gallon (of the entire system) You can add two pumps and two airstones in each bucket.
 
3)  Yes, those are the buckets!

 

 
Hi Plucky!
 
I didn't have any problems with mine, but I built a paper template that I folded and taped up, so it fit the bottom of the bucket just right, and had a spot I used to park each bucket where I was to drill my large holes.  This kept them all the same height.  This is important because if you have one bucket cut too high or too low, it will cause stress on the uniseal connection, and eventually a leak.  This was apparent and obvious to me prior to building my system, so it wasn't an issue for me.  As long as you're aware of it, and make all your holes in a consistent manner, this won't be an issue for you. 
 
Some folks definately have trouble assembling one of these systems.  I would suggest purchasing several extra buckets to practice drilling on first.   You can make 10-12 holes in one, just to practice drilling in that type of plastic.   Focus on drilling slow.  SLOW SLOW SLOW, so your cuts are even and round.   I bought a nice hole saw bit in the size I needed for this, as my normal hole saw set is a Harbor freight cheapo.  I bought a name brand hole saw that cost more than the entire HF kit, and it was worht the extra investment to cut nice true holes.   
 
Thicker buckets would have a better integrity, and probably be easier to machine/fit with uniseals.   As long as you're careful, and clean the cut holes nice and smooth, you'll be fine.   It takes a little practice, and you'll get better at it with each hole you drill.
 
Keep us updated!

 

Hi Plucky,
 
Sure thing!   Since controlling the oxygenation of your nutrients is key in a DWC, it's important to use nice air stones.   Most important factor is the power of your air pump.  Next, you want a stone in each plant site, and I put a huge one in the controller bucket.  All powered off the same pump.
 
What's important about multiple airstones on a single pump is that they should all be of equal depth, below the water surface.   Otherwise, most of the air will escape from the most shallow stones.  The deeper stones will have less air flow through.  This is due to the water pressure caused by gravity.  So number one, get some fish tank suction cups, and stick your stones, or the lines down to the bottom of your buckets. 
 
What I did, and looks confusing is make my own air manifold.   The use of a manifold is to allow equal pressure to each of the airstone sites.   As long as your stones are placed at equal depth, this is pretty easy to achieve.  My manifold is simply a small chamber (size is unimportant) that air flows into, and then is split into multiple paths.  You can purchase one, but I like to build my own parts, and I had most of the stuff laying around.  I used a scrap of the 2" PVC and glued caps on either end (drilled a hole in one first, to allow air out, to get a tight fit)  Then I drilled 5 holes in the body of the PVC and glued and sealed 1/4" nipples in place.   I glued a 5/8" nipple in the end of one cap, this serves as an input from the air pump.  So the airpump uses a 5/8" line to feed the manifold, and the manifold has 5x 1/4" lines feeding each of the airstones.    I experimented with standard 3/16" air line, and have found that the 1/4" flows much nicer, because I have a very powerful air pump.  If you uses several small pumps, 3/16" line is fine.  
 
Two more points, I would like to make.
 
1)   I would suggest drilling holes for your air pump in the bucket, rather than the lid.  If you can pull up the lid without disrupting the airstones, your maintenance tasks are much  more simple. It's also easier to keep all the stones at equal depth.  
 
2) lightproof your airline at the point it enters the bucket.  You don't want light to enter your reservoir, period.  The hole where the tubing enters (especially if you use clear tube) is a great point where light can enter, too.  I made little flaps of duct tape that simply cast a shadow over the hole.  Low tech, but effective. 

 

Hi FarmerJames,
 
I ran into the same problems that you describe.  Ultimately, I chose to abandon the recirculating DWC system for more efficient methods.  
 
That said, with the right buckets, and carefully drilled holes, I did have success in building a solid system.   You just have to be real careful about not moving anything, especially while it's full.  This causes a lot of stress on the system, and causes fractures in the buckets, resulting in leaks.