Determine the lowest point in your pond if possible. Dig the bottom of your pond at an approximate 30° downward slope to create a small area where water flow will cause debris to collect.
Install all necessary drainage pipes including a 3" ABS elbow (90°) directly underneath the lowest point in your pond. This is where the bottom drain will be installed.
Install the lower half of the bottom drain at the predetermined point in your pond, attaching it to the ABS elbow pipe with ABS glue available at plumbing supply and hardware stores, and home centers. It is important that this connection is totally secure. When this step is complete, the installed piece should be recessed at least 3/4" below the level of the pond bottom.
Install your 45 mil EPDM liner. After your liner is fully installed, locate the spot where the lower half of the bottom drain has been installed underneath the liner, and using your fingers, find the six screwholes located in the gasket and rim of the bottom drain lower half. With a white pencil mark your liner with the location of the screwholes. Using an awl of leather punching tool punch through the liner at the pencil markings being careful that the diameter of the punched hole is not wider than the diameter of the screwhole in the rim of the drain underneath the liner.
Apply a light coating of silicone sealant to the liner in the circular area directly covering the drain. Then align the screwholes in the upper half of the bottom drain with the holes punctured in your liner, and using the six flat head machine screws provided attach the upper half to the lower half. It is important that the studs on the rim of the upper half of the drain should point upward, the flat surface of the rim should be flush with the liner. Do not overtighten at this point, the liner should be firmly sandwiched between the halves of the bottom drain, and the rim of the upper half should be level or slightly below the bottom of the pond. This will create a final drop into the drain.
Once the halves have been securely joined, carefully cut away the circular portion of the liner inside the drain, making sure to trim the liner flush with the inside edges of the drain. Apply a light coating of silicone sealant to the inside surface of the drain.
The white gaskets on the two halves of the drain are made of closed cell material. The resulting compression of these gaskets against the liner provide a water tight seal.
Fill the drain cover dome with pea gravel or aquarium gravel until nearly full, then glue the plug using PVC or ABS glue into the bottom of the cover.
Align three studs on the bottom of the cover with studs on the rim of the upper half of the drain and insert. Press down until securely sealed. Do not glue or cement in place! The cover dome is meant to be removable for cleaning.
The shape of the cover dome is designed to force debris and water to flow into the drain inlet. Do not place potted plants, stones or decorations to the bottom drain in a manner that could impede proper water flow.
Periodically remove the cover dome and inspect drain for blockage.