Well this is what I came up with. Bottom of a 5 gallon bucket cut like this. We used a 3/4 T with 3/4 electric conduit with 3/4" threaded fittings on each end. The hole through the bucket is 1" to let the conduit through. The conduit threaded end is larger then the hole. So the part will not come off the bucket. Then the one end is plugged and the air line hose barb on the other.
We will fill the bucket with some cement. Thinking of a few bolts in the bottom connected with wire, so when the creet drys it will not just pop out like a mold.
The air head can tip just in case the bottom of the pond is not level or we land on a rock. Should work good.
Cheers Don.