Of all the components to an above-ground pool's mechanics, the one that anyone can build himself is a filter. Anyone with basic plumbing skills and access to pool sand can accomplish this in a matter of hours. A pool's sand filter works by trapping contaminants and particles between the grains of sand as the water enters the filter and then preventing their release into the swimming pool. As more particles get trapped in the filtering sand, the less space is available between the sand particles and the sand filter traps even more unwanted debris.
Place the plastic container next to the pool's pump. Make sure that it is in a convenient location for both filling it and eventually cleaning it when necessary. Make sure it is out of the way of passers-by who may accidentally knock it over.
Drill holes in the container for both the incoming and outgoing water. One hole should be drilled in the center of the lid and the other about half an inch up from the bottom of the container.
Attach the mesh or nylons to the ends of the incoming and outgoing water supply hoses. Make a tight seal with the plumber's tape or stainless steel clamps to hold the mesh to the hoses.
Insert outgoing water supply line hose into the bottom hole of the container. Apply silicone or other waterproof caulk to the space between the container and the hose to create a seal.
Fill the container three-fourths of the way with the pool sand.
Place the lid atop the container and insert the supply line into the top. Use the silicone or waterproof caulk again to create a watertight seal.
Test your pool's filter. Turn on the pump to see if there are any leaks in your sand filter. Use caulk as necessary to repair.
Check the sand in your filter regularly. Change it when it is green to black in color.