I am building two ponds. I am installing a 4 inch Auto Siphon on Pond A. Pond B will be 75 yards away on a downward slope. Can I run my 4 inch PVC pipe underground so it flows into Pond B (3-4 feet under water level)?

Don’t know why it couldn’t work

On the drawings I've seen, the very end of the pipe where the water comes out has a series of connections that shoot the pipe up. What is the purpose of that?

Don't know unless for aeration. And, it generally does a poor job of that.

I just assumed it was to keep the erosion down by spreading the water stream out.

I think I read somewhere it is to seal it so it wouldn't keep hammering, but I cannot find where I read that.

The reason for the pipe turning up at the exit is to create an air lock. If not the air comes in from the exit and can't reach a full siphon. I had that problem in my first siphon system until I extended it up enough to create the air lock at the exit. It also helps aerate the stagnant water before it reaches the creek.

OK. I think if my exit pipe runs underground to a new pond and the exit is 4 feet under water the same purpose is served (sans the aeration).