I need to drain my 70 year old, 2 acre catfish pond so i can excavate the several feet of muck at the bottom. It has an overflow drain which I believe is 6 inches. I don't want to break the dam so I am trying to decide if I can siphon through the existing overflow drain or spend $1000 and build a natural siphon system out of 6 inch PVC over the dam. Anyone have any experience siphoning through the overflow drain? Most of the catfish have died out and the goal is to fill the pond back up and introduce some kind of bass into the pond.

Is the 6" overflow pipe something you can directly connect to another pipe? (For example, is it clean PVC or 70 year-old rotting galvanized steel?) You can certainly use your existing pipe if you can make tight connections. However, air leaks are the enemy of siphons.

If you can't do it that way, then over the dam with flexible corrugated pipe is pretty cheap and easy.

Here is a link to a video. They aren't rocket scientists, but do show all of the key steps.

Pond Siphon

You may need a trash pump to get the last bit of water out of the pond. And it might be very valuable to get that last bit!

If you are re-starting your pond with new fish populations, it will usually be much cheaper and easier to manage it with ONLY the fish you have introduced.

Draining it completely dry for several months would work, or you may have to exterminate with a rotenone treatment.

Of course, all of that may be pointless if the water source for your pond can easily bring in undesirable fish species.

Good luck on your pond renovation project!

what siphoning directly into the existing standpipe??? Imagine a very tall upside down "U" with one end in the pond and the other down the stand pipe. Not sure if it would even be possible to get that siphon started.

I've never had any issues with the water level going down so I'm assuming the steel pipe is still pretty solid. I guess I will start by trying a U shape siphon trap and connect it to the pipe. Do you think I could get away with using corrugated pipe for the siphon trap and connect that to the steel pipe or should I go with PVC?

PVC. it's a lot easier to connect waterproof and air proof fittings to it.