Check out the AMAZING airlift video! I have checked (with a manometer) and about 0.2 psi has pumped water to over 6 ft high. (It worked all night using 3/16 inch tubing). The whole pallet planter thing works great after a few modifications to the original idea! As you work on them you discover things and adapt. Originally, it was going to be just one pallet standing up. So now they are 2 pallets joined together (to get a decent 7 inch gap) and the pallets have legs to stand on and the legs collect water in their "boots" to be recycled back up top again. Also, the floors of each section now slope back. The concrete on the bottoms of the "boots" is to prevent the weight of the pallets breaking the plastic buckets.
Step 1: Concrete Shoes for the Good Guys!
This step looks hard but it really isn't. If the plastic of the base of the bucket takes all the weight of the planter and moves, it will break and leak. So you need to make strong concrete round the base. In this case, I made the concrete using wet masonry sand as a sand mold and a flower pot that is a bit wider to make the hole in the mold., I used a pallet with plywood under the sand and then a 3 to 1 mix of coarse sand and cement for the concrete of the foot. So lots of pictures and a few image notes to explain the steps. The pictures are screenshots from a camera movie so not wonderful quality but its better than watching my youtube movies! As I write, they are curing, it is cold so it will be a while. BUT, I have already made one pallet planter to a slightly different pattern and that first one does not have the feet at all. I haven't used a sand mold in years but it works great. (Your sand has to be just the right firmness and wetness. If it sumps too easily you may have to add a portion of clay. (if you have clay!)