This web page has pictures and instructions on how to utilize a 4" bottom drain in a pond. It is recommended you use one drain for every 12'diameter of pond floor. If your pond is 12' x 12' one bottom will handle it nicely if the bottom of your pond has a smooth surface and you draw the maximum flow through the pipe. It also helps if you bowl the bottom of the pond so it slopes to the bottom drain(s). I made the drawing for a client that was going to be pumping the water to one of the stock tank waterfall filters. By removing the majority of the larger solids from the water before the biological filtration the biological filter media remains much cleaner and therefore more efficient.

UPDATE:  July 21, 2006 we added photos showing all the steps to install a bottom drain.  Scroll down below the drawings.  I hope this will help with your bottom drain installation.

Our commercial site:  http://www.koivillage.com

The drawing at the top of this page shows the bottom drain feeding a Nitritech Vetech vortex. This drawing shows the bottom drain feeding a filter box. You can build the filter box from a heavy plastic container or use one of the commercial filters designed for this type of flow.

The drawing below shows the same set-up with the Koi Village modified bottom drain to add an air diffuser. The air inlet is through the bottom so their won't be any air lines to obstruct the flow. We are having these modified by a plumbing fab show and it will take some time (money) to have a regular supply. We are now selling them as fast as we can get them modified. The inlet at the bottom is a 3/4 female threaded (NPT). We will be supplying a 3/4" female x 1" socket (slip) fitting. This will allow the air supply pipe to come from any direction.

Below are photos showing the steps required to install a bottom drain. The one being installed is one of our Koi Village bottom drains we've had modified to include an air diffuser with check valve. This is the standard 4" ABS bottom drain we have sold since 1999. Hopefully we will soon have a source for a 4" diffuser bottom drain that has been molded to suite our requirements and we won't have to make any more ourselves.

The installation is on a 1,000 gallon tank the we use for quarantine and holding tanks. This tank will be used primarily to test different filters that are compatible with a 4" bottom drain.

Once you've excavated the hole and trench for the pipe make sure the bottom
drain and pipe are level.
 

Below are photos showing the steps required to install a bottom drain. The one being installed is one of our Koi Village bottom drains we've had modified to include an air diffuser with check valve. This is the standard 4" ABS bottom drain we have sold since 1999. Hopefully we will soon have a source for a 4" diffuser bottom drain that has been molded to suite our requirements and we won't have to make any more ourselves.

I'm using one of the regular 4" ABS bottom drains that we have modified to include an air diffuser. Anytime you glue ABS to PVC you will need to use the “All Purpose Glue” for ABS and PVC. It will indicate on the can that it is for both.
 

The photos below show the bottom drain after the concrete was added. This will prevent the bottom drain shifting and pulling on the liner.
 

I used the white tarp shown in the previous photos for the underlayment. I prefer using the geotextile underlayment, but didn't have any and I didn't want to wait for it. This tank along with the others outside will be removed within a couple years anyway.

These are the tools needed to install the drain through the liner. Utility knife to cut the liner, small nail to puncture the liner for the screws, screwdriver, screws, and clamp ring. Be very careful with these sharp tools while in the pond. It is safer to put all of them into a bag or bucket so you don't accidentally lay one down and step on it. That may puncture your liner in a place not intended.
 

Use a utility knife to cut around the inside of the bottom drain sump. Lift the liner up so you can see the holes for the screws and use the nail to puncture the liner for one screw and then again on the opposite side.

Before installing the clamp ring put a bead of the sealer of your choice around the rim of the bottom drain in front of the screw holes and press the liner down gently. I like to use the "Plumbers Goop".
 

Place the ring over the bottom drain and start the screws in the holes you have made. This will insure that all the other holes are lined up correctly.

Now you can use the nail to puncture all the other holes for the screws.

Tighten all the screws just enough so they are touching the top of the ring and then start tightening one at a time working from one side to the other so you get equal pressure all the way around the ring. You need to go back and forth several times. Once all the screws are hand tight you are done with this part.

If you are using an aerated bottom drain connect anything needed for the air.

Use a shop vac to vacuum out any debris that have collected in the bottom drain.

 

Install the dome and you're finished.

I use "tees" instead of "elbows" for the connection to the filter so I can put in another valve to be able to drain the entire tank when I want to. It is also good to have so you can flush your 4" pipe to remove any debris that may have settled in it over time.

 

After the tank was filled. It is 3' deep.

 

I'm using a Dolphin AV50 air pump.