Several types of pool filters exist. The most common are cartridge or sand filter types. The easiest to construct yourself is the sand filter, which utilizes know-how that has been employed for many centuries. Essentially, the incoming water is run through a tank filled with sand. As larger particles are trapped, it becomes increasingly difficult for smaller particles to pass through and eventually only the tiniest of debris particles will be filtered through into your pool. Some basic mechanical knowledge and the right tools are all that's required to construct your own sand filter.
Set the container next to the pool's pump. Place it at a location that is convenient for you to work on and out of the way of pedestrian traffic.
Drill two holes in the container. One should be about ½ inch up from the bottom of the tank, and the other should be in the center of the lid.
Apply mesh or nylon to hose ends with plumber's tape or stainless steel clamps. Put pool hoses into drilled holes. Make sure there is enough slack in the lines to be able to lift off the lid and adjust the filter slightly if necessary.
Apply water-proof caulk around the hoses and holes to create a tight, leak-proof seal. Silicone caulk works well for this.
Fill the container three-fourths of the way with pool sand. Pool sand is of proper coarseness for filtration, and other types should not be used.
Test your filter. Run the pool's pump to make sure that there are no leaks. Use caulk as necessary to repair.
Check your sand periodically. When it is a green to black color, it is time to replace it.