Most building codes require that all pipes in a pond that will be either under ground or inside concrete need to be pressure tested before they are covered. The reason for testing these pipes is because repairing a leak in one of these pipes after the pond is finished is very difficult if not impossible. Pressure testing these pipes is well worth the extra effort and expense.
First, install all pipes leading to and from the pond to the equipment area. This includes the pipes for the bottom drains, skimmers, jets, waterfalls and any air lines. For concrete ponds stub all bottom drain and jet pipes out into the pond an extra 12 inches and then cap off. (For liner ponds, install the proper bulkhead fittings on all the jets and then screw in a 1 ½ inch threaded plug into each bulkhead. Make sure to Teflon tape the plugs. Extend the 3” bottom drains up into the pond and cap off. After testing you can come back, cut the cap off and install the proper bulkhead fitting.) Connect any skimmers to the appropriate skimmer pipe. Most skimmers will have a screw in plug that you can Teflon tape and then screw into the skimmer to plug the pipe at the skimmer. Cap off any air lines for bottom drain diffusers if installed. Once all the pipes leading to and from the pond are capped off you will need to connect all these pipes together near the equipment area. By using a combination of tees, elbows and reducers connect all these pipes together leaving one end open so that you can glue on the pipe pressure tester. (See picture)
Allow the glue to dry for at least 1 hour. Open the ball valve on the pressure tester and then connect a garden hose to the tester. Turn hose on and allow the pressure in the pipes to reach 30psi. This usually takes several minutes. When it reaches 30psi on the gauge, close the ball valve on the pressure tester assembly and then turn off the hose. You can now disconnect the hose from the pressure tester assembly. The pressure should stay at 30psi. Leave at this pressure for several hours to make sure you do not have a small leak. If the gauge does begin to drop slowly, check the plumbing for leaking water. First check any threaded joints where you used Teflon tape. Especially check the threaded plug on the bottom drain pipe cleanout if you installed one. If you find a leak you will need to release the pressure by opening the ball valve on the pressure test assembly before you make the repair. Then make sure to test the system again.
On concrete ponds you may want to leave the pipes under pressure until after the concrete is poured or the gunite has been shot to make sure no pipes were broken in the process. On a liner pond, after pressure testing, you will need to cut the ends off the pipes leading to the bottom drains so that you can install the bulkhead fittings for the liner.