The purpose of a koi pond bottom drain is not so much to drain the pond as it is to remove the debris from the bottom of the pond into the filter where it can be removed from the pond system. The bottom drain should be drawing water into the filter 24 hours a day. With this purpose in mind, koi pond drains have a unique design. They need to allow leaves and debris to pass through it without allowing the fish to be sucked up at the same time. The most successful type of drain for this application is an open drain with a cover over it. (see drawings)
This type of drain has been very successful in the past but it has its short comings. One problem is that it can be hard to service if leaves get wedged between the drain lid and the pond surface. If you lift up on the drain cover to allow the leaves to pass through and the lid comes off, it is impossible to reinstall the lid without going into the pond. That is a real problem in a deep pond, especially in the winter time.
Another problem with this type drain is that they can be hard to install. If you are building a concrete pond you will need to accurately estimate exactly where the bottom contour of the bond will be so any debris on the pond bottom will gently flow into the bottom drain. If you plumb the drain too high or too low it will greatly reduce the efficiency of the bottom drain. (see drawing)
The final problem is that it is very hard if not impossible to pressure test this type drain after it is installed. You can install a balloon type plug in the line but our experience has been that it is very hard to get them to hold 30psi for testing.
If debris begins to collect around the Advantage Bottom Drain Cover you can simply reach in the pond with a pool pole and net and slide the cover to one side, dislodge the debris and then slide the cover back over the bottom drain hole. (The Bottom Drain Cover with air diffuser has a hose that connects it to the air supply which is flexible enough to allow you to slide the drain to the side without disconnecting the air pipe from the cover.)
With most other type bottom drains it is very hard, if not impossible; to plug the bottom drain pipe for pressure testing once the drain is installed. With the Advantage Drain Covers on concrete ponds you can simply stub up the bottom drain pipe, cap it off and once the pipes are pressure tested, leave them under pressure until the pond is completed to make sure no pipes are damaged during construction. The last thing you do, after plaster and before adding water is to cut off the bottom drain pipe level with the pond bottom and place the drain cover over the pipe.
Installation instructions for Standard Drain Cover in concrete ponds:
For concrete ponds simply extend bottom drain pipe vertically through concrete and cap for pressure testing. Make sure concrete around drain pipe is level for at least a 9″ radius. This will allow proper clearance when cover is installed. After concrete is plastered, simply cut drain pipe off flush with pond bottom and place drain cover over drain hole.
Installation instructions for Standard Drain Cover in liner ponds:
For liner ponds remove dirt around bottom drain pipe 6″ deep with at least a 9″ radius. Install the bottom drain bulkhead fitting 1″ below the pond bottom surface. Pour concrete in area around bottom drain and contour as per the following drawing. Let the concrete dry, install liner and then place drain cover on liner over pipe opening.
Note: Placing 6″ of concrete around the bottom drain will help to keep the bottom drain from floating upward if in the future the pond water was lowered and the liner began to bubble up due to ground water behind the liner. This could save you having to tear up your whole liner if the drain got dislodged.
Installation instructions for Drain Cover with Air Diffuser in concrete ponds:
Follow instructions for standard drain cover except add a 3/4 inch PVC air line extending into the pond 12 inches from the center of the drain pipe. Cut pipe 1 inch above concrete and add a 90 degree elbow. Add a 3/4 to 1/2 bushing to the elbow, then glue a short 1/2 inch nipple into the bushing. Proceed to connect a 1/2 inch line to drain cover with the plastic hose included with drain cover.
Installation instructions for Drain Cover with Air Diffuser in liner ponds:
See Bottom Drain Installation.