Yes, the electrical cord that plugs in goes to a small relay inside the pump. As long as the cord is plugged into the wall, the set of contacts that completes the circuit to run the pump from the D cell batteries are held open. Once the outlet the cord is plugged into loses power, the contacts close, completing the battery circuit et voila, the pump runs on the batteries. Similar concept to what happens in a UPS, but much simpler.

As for the air lift, the wiki I linked to doesn't explain the principle well enough?? The only difference in the article graphic Figure 1 is that they have the air supply line feeding through the vertical tube at the bottom through a bulkhead. My gizmo photo has the air supply tube fed through a hole in the top of the elbow. Works the same way. Of course the wiki article also goes on to show the modified/improved geyser version. The advantage to the version in my photo is the air tube can be adjusted up or down inside the pvc tube to fine tune the air lift effect. The version shown in wiki with the tube entering the bottom in a fixed position does not allow for that.

EDIT: One more thing to note, although I did explain in my original post about airlifts, is that in our case, the opening of the elbow at the top of the assembly will be half submerged. In the wiki figure they show the elbow above the water surface. Their application has the water being pumped/lifted out of the tank. In our case, with the elbow half submerged, the water is discharged back into the tank at the surface, creating a moderate flow.

Here's a link to one of the better vids I can find on the workings of an airlift. A bit lengthy, but should leave few questions unanswered. These things clearly have a lot of applications. Most of us likely have the parts needed kicking around the house already, so not a lot of effort to slap one together & see how it works.

https://youtu.be/_j0tmCc5Z3Y

In essence, the construction is similar to an air stone skimmer. Micro bubbles in the skimmer pick up organics & transport them to the surface, the air lift uses larger bubbles to bring water to the surface more effectively. The elbow at the top either discharges the water back into the container, or out, depending on the application. I wonder if a venturi part way up the riser pipe would improve lift efficiency.... a patent in the making??

Here's my skimmer, shows the rigid airline inside the skimmer body, same idea for my version of the airlift:
https://tsl4pa.bl3301.livefilestore....15d.jpg?psid=1