You simply cannot build a good pond without a good liner because it is the skin of the pond and one of the most important components of The Docs Dream System. The object is for the liner to last 20 years.

Run as fast as you can away from preformed ponds. We suggest and use exclusively 45 mil EPDM liner material. Liner material is priced by the square foot and is cut from any of these widths to the length you request. Find more information about liners by reading our article “Liner vs Liner” in the Water Garden Edition.

Here is how to get the correct measurement for liner:

Drop a piece of string 18” from the edge of the pond where the water will crest. Drop the string along the hole at the widest part, allowing it to follow the curves of the hole then mark the string 18” from the opposite edge. Now measure your string. Do this also for the length of your pond.

If the hole that has been dug has any rocks, pebbles or roots in it and is not as smooth as a babys behind a pre-liner or underlayment must be installed to protect the liner. Commercial underlayment is available. We do not suggest sand. It shifts underfoot and can render plant shelves useless. Old carpet can also be used. Roll out the underlayment and cut out holes where the bottom drain and other components are to be installed into the liner. The Koi Pond Guide has underlayment for sale click here to email me the size you need.

The bottom drain, skimmer, induction jets and plumbing must be installed before the liner can be laid. When it is time to lay the liner lay it smoothly. Wrinkles should be pulled out, corners folded and neat. Even as the pond is being filled with water the liner should be continually adjusted. Sharp objects have no place in this part of the installation. Keep dogs away and go barefoot if possible.

A Bottom Drain in a pond system does not mean simply a device to drain the pond of all water. It is the way to pull the water from the floor of the pond and re-circulate it through the outside pump and filter system before returning it to the pond.

2” Bottom Drain

This white PVC drain is fit with a 2” opening to the pump. The bottom part must be plugged for our purposes. It comes with a regular grated white plastic cover and an anti-vortex cover. The regular cover is great for a water garden pond that has no fish. If the pond is to hold fish, especially small ones, the anti-vortex cover is the best to use because it does not suck fish up to the grating. The drawback to this drain is that it does not allow leaves and debris to pass through to the leaf catcher of the pump making it necessary to scoop the bottom drain occasionally with a net to get the fallen debris.

3” Bottom Drain

This black domed bottom drain has a 3” opening to the pump. It should not be used if there are fish smaller than 7” in the pond. The dome sits about an inch over the floor of the pond and will literally suck small fish into the plumbing system. The good thing about this bottom drain is that it sucks up large leaves and debris and brings it up to the leaf catcher of the pump making it unnecessary to scoop off the bottom trash.

4” Bottom Drain

The 4” bottom drain is similar in design to the 3” and is used on very large ponds.

Inverted Bottom Drain

This is not a true bottom drain because it is not installed directly into the liner. It is more of a caged box that is attached to flex hose and allows water to be sucked from the bottom of a pond. This is an excellent choice for those who are converting an existing pond to a cleaner system.

Bottom Drain Installation Tips

While digging the pond a hole must be dug at the deepest part and furthest away from the water return for the base of the bottom drain. Place the base in the hole. Make sure the base of the bottom drain is level and the top of the base sits about 1/2” below the floor of the pond. Run PVC plumbing to the bottom drain. If the pump is to be placed higher than the water level of the pond somewhere into that stretch of PVC pipe, perhaps the part going up the side wall of the pond, install a check valve.

Component 2a - Check Valve

The check valve assumes a very important role. Whenever the outside pump is installed above the water level of the pond unless a check valve is installed every time the system is shut down the pump will lose its prime. The check valve prevents the water in the plumbing from flowing back into the pond. It is very important that the check valve is installed in the right direction otherwise it will prevent the flow of water into the pump!

Once the liner is down the top piece of the bottom drain is installed. Two gaskets are included with the 2”, 3” and 4” bottom drain kits. One gasket goes between the bottom piece of the drain and the liner. The other gasket goes between the liner and the top piece of the bottom drain. Using your fingertips you would feel through the liner for screw holes and attach the two pieces together with the liner in between. A hole is cut out of the center of the bottom drain after this is accomplished. The only thing left to do is place the cover of the drain on the 2” bottom drain or the domed lid on the 3” with screws provided in the kit. Note: The dome on the 3” bottom drain should be filled with sand to prevent it from floating.

Resources: This article is from the Pond Doc's Website.