Correct me if i'm wrong.. Your inner wick pot is upside down, but the reservoir pot is not.  Correct?  What's above the reservoir?

Correct. Picture a 5 gallon bucket (solid) upright with an upside down 2 gal bucket inside (perferated). Both pots at same height (level) At the very center would be clean water, the reservoir. Outside of that pot, between that pot and the 5 gal bucket would be my wick of soil and water. Above all of that would just be soil. No need for mesh seperation.

ahhh... i had it backwards..  i thought the very center was the wick.  I'm with ya now.

So the "funny" pipe will run from the center instead of where I put it in the picture above.  That's actually pretty clever.  Is the inner reservoir much smaller than the 5 gal?  I'd try to get one that is about 4" narrower in diameter.  That will give you about 2" ring for the wick and maximize the reservoir space.

Keep us posted on how it works out!

Now were on the same page. I'm with ya! (I noticed that you had the drain pipe stuck in the dirt). What I realized is that water would get some floating stuff in it and may clog a 1/2" pipe so a 1" PVC would be better.

But now that that's hashed out, here's another idea. If you did not have the 6" perf pipe you could suspend a 2 gal pot by it's rim in the center. Pop it full of 1/4"-3/8" holes and you're good to go.

(Yes my drain pipe should be higher in the bucket towards the lid. Lol)

Yep.. that should work too. 

Aaron,
Since you are starting with existing perforated planters, an idea may be to fabricate a simple Multiflow Hydronic System. All that's needed is one (1) level controller bucket (with float valve) and multiple wicking buckets. The wicking buckets are filled with sand and would be wicking and watering reservoir all in one. They would be placed inside the planter. In the attached video you will see the concept. All that is necessary is a "Level Controller bucket" with an installed float that is attached to your water supply.

I don't plan on covering the pots with plastic to keep out rain water. Because there are drain holes on the bottom of the 20 gal pots, I don't see the need. I will be irrigating all of the pots with 1/4" drip tubing. I currently have 150 pots with about 80 varieties with no plans of slowing down. Paying $30 each for SWP's or even $15 is getting out of hand. I already have to up pot 1/2 of my figs. The soil and fertilizer alone is enough.

Pete. I don't see (at all) how that would be easier. I have very low cost or free materials and an existing irrigation system. Also, my pots do not all sit level, there is a slight hill. All things being equal and I had a huge level area that I kept them on and money was no object, I'd have them on a flood table regulated with moisture meters. Sorry.

I think the plastic on top is not just for keeping out rainwater.. it also reduces evaporation, so the top half of is staying too dry.  It keeps it consistent. 

Aaron,
The remote reservoir of the multiflow system is much easier to fabricate than individual multiple wicking / reservoir buckets and the containers could be grouped together to share a common level control bucket. Similar to a multi container Autopot system.
    
But, for your application the wicking/reservoir buckets can be built like the individual Alaska Grow Bucket and then water can be added (by your existing irrigation system) through the fill tube. The Level control bucket and its associated tubing would be eliminated, Similar to your design No. 2 in post #17 or the picture in post #24 or post #30. Good Luck.
 

Please keep us posted on your final design and implementation.

<edit> For a 24 inch Diameter (452.4 sq.in) container the cross section for the wicking tube should be approximately 8 inch diameter (45.2 sq.in).
18 in Diameter container...6 inch diameter wick tube.
12 in Diameter container...4 inch diameter wick tube.

Aaron, did you ever end up converting a 15-20 gallon nursery pot with holes to a SIP?  I would be interested to hear about the design you finally came up with.

Hi Adelmonto,
I hope your inner bucket is strong enough to hold the pressure from the dirt around it.
I hope your holes don't clog up.
To be honest, I don't see the purpose of the inner bucket .
Is your climate hot ? That would help dry the mix in the pot.
Is your climate not rainy ? If rainy, you'll be washing the dirt and losing the nutrients through the overflow - so definitively I would want to put a lid on the pot .
What is the height of the pot ? At a certain height the wicking power of the dirt will be inefficient to return the water to the surface of the dirt.
IMO, the key would be to put the pot on a sunny spot. If the pot is in a shady spot, I would expect the dirt to turn soggy and moist .

I've tried something like that with just putting an open bowl in the bottom of at tub as a reservoir. I couldn't tell when it was full and when I up potted I found that the roots had rotted in the reservoir. I have some 30 gal. tubs I use for small plants, peppers and such. They already have drain holes and I have been thinking of retrofitting them with a reservoir, but with closed top, feed and overflow tubes, and a net bag (like in the rain gutter system) for a wick. I would line the tub with weed excluder cloth because I've seen a site selling commercial pot liners that they claimed acts as an air pruner and stops root circling even though it's up against the side of a pot. I wouldn't use a 5 gal. bucket though. I'd cut a 2 or 3 gal. bucket off at 4-6 inches to give more root room above it.

I just found this link describing one approach to convert a container with holes to a SIP:

http://www.insideurbangreen.org/2011/07/converting-drain-hole-pots-to-sub-irrigated-planters-sips.html

Has anyone tried this?