If you push air, I would mount the compressor up off the ground by 2-3 feet somehow, and have the line come out of the compressor, dip down, and then go up to the pond. To make a "P" trap of sorts in the airline and plumb in a drain there. You will want to open the "P" trap drain to remove moisture from the line. If the moisture builds up enough to go into the compressor when it's shut off and you don't catch that , the compressor will most likely be locked up the next time you want to fire it up.

Yes, there are check valves in some systems and you can put one in, but mechanical things fail. In this instance, I think you are better to run electric to the pond.


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