I picked up a 40gal aux tank from Craigs and hooked up the gravity feed this weekend; will try include pics.
1. I used the kit from Northern Tools. Seemed a bit expensive ($70) but it worked good.
2. I cut the filler hose so that the kit would be as upright as possible per instructions with the kit. This is in order to not have the tank overflow/fill. There's a little "ball-float" in the bottom of the feed devise that prevents fuel from flowing when it gets close to the top (pretty sure I didn't say that right, but...it works).
3. When installed in the filler tube correctly, it sits upright. (see pic I hope)
4. Next I had to decide where to drill out the hole for the hose coming from the aux tank to go thru the bed. I also didn't want the hose rubbing on the metal-bed-hole, so I needed something to protect it. I looked around the garage and found a garden hose mending piece...you know, if your garden hose connector is damaged you can replace it with a new insert (sorry, I'm not doing well with describing today...see pics I hope)
((I've maxed out pics, so will continue with Part II next thread posting)

 

....next, FILTER. I was pretty confident that the used tank was clean, but wanted to make sure. I also did not want to go with a fancy set up of filters and separators (on a budget). So, I still knew I wanted a filter. So, I went to ebay and found a diesel fuel filter for a Mercedes !! Looks kinda like a lawnmower fuel filter, but hey, if Mercedes uses it, I figure my DODGE CUMMINS TURBO could use it... (see pic)
The rest was pretty much just making the hose connections and ensuring the clamps were snug. Guess what---IT WORKS! Trust me, I'm no mechanic, so I'm fairly proud of myself. I then filled the tank and added a couple ounces of "biocide" just to be sure the tank didn't have fungus in it (visual check looked just fine, but didn't want to take a chance...thus the "catch" filter just in case too).
I tested the rate of flow thru the on/off valve I have set up (used a long stick for rough idea) and it turns out that my tank gravity feeds about 10 gallons into the tank in about 30 minutes. That's with the valve wide open feeding into the stock tank that's about 1/4 full.
My aux it just a temporary set up; since it's only a 40 gallon tank I'll likely just use it if we go on long trips (only 1-2wice a year). But I like it allot!