Next it was time to try the outside filter / skimmer idea. The major reason for this idea, was to keep the filter outside, so I could access it to clean / service without having to open the cage door. My problem was what to build on the outside, thinking of basically another very small pond. I bought a 'rope basket' (that's what they called it) at Big Lots for $4, which was the perfect size. I cut a slot in one side, and attached the pond liner to it. I had to drain the pond below the level of the slot, to let the silicone dry. That night, we had a LOT of rain, and the pond level came up past the bottom of the slot, so it did not get to dry fully. Sure enough, it did have a leak; just a drip, but a leak nonetheless. I bought some marine epoxy, and sealed it up, even wet. You can see the Jacuzzi filter which is just lays on the ground on the bottom left.
When the water level is real high, the water comes in both the top and bottom of the prefilter bucket. If the water is down a little, it doesn't come in the top. I was trying to be 'professional' in my sizing quest for the outside tank, but called it a little too close. That doesn't really matter, though, as more than enough flow can get in the bottom. It actually even helps, because the floating waste (like turtle poop) doesn't get sucked right into the filter media, but just floats around in the outside bucket for easy skimming.
Once the filter starts getting dirty, though, I noticed the bucket started floating up a little. With the pump pulling all that water out, it is not always absolutely full. So for now I threw the cement block on top, to keep it tethered to the bottom. There is a 1" pvc frame beneath the bucket, so that the bottom of the filter bucket is not right against the bottom of the big container.
As you can see from the inside, there is a 1" PVC double tube running through the 'slot'. This is not really intended for the water to flow through, but rather to hold open the slot, so the pond liner doesn't fold in onto itself and block the flow. It especially holds it right to the bottom of the slot, as this kept wanting to 'ride up. This system works REAL well as a skimmer, as basically it is mostly taking water right off the top of the pond. I did add the 'down pipe' to the bottom pipe on the inside, as some water does indeed flow through the pipes, and this way I am picking up some 'bottom water' also. I don't really think this matters, though, as I have tremendous water movement / mixture due to the drop of the waterfall, and the relatively high water flow.