The basket strainer in the pump is really the second line of defense when it comes to gathering debris too large for the filter to handle. The first is the surface skimmer.
The skimmer draws in surface water and whatever resides on that water (oil, leaves, and windblown dirt or other debris) and collects large material in a basket, much like the basket strainer in the pump. The skimmer keeps the surface of the water clean and minimizes the amount of debris that makes its way into the main body of the pool water. Most pools have at least one surface skimmer, and some have more. The skimmer is located in the waterline tile on the downwind side of the pool.
If you are considering constructing a pool or spa, keep in mind that a skimmer is most effective when located on the downwind side of the pool because the wind directs the water (and debris) toward the skimmer.
There isn't much to maintaining a surface skimmer other than making sure to empty the basket at least once each week -- more often in the fall when leaves are a problem.
Often the interior surface of the skimmer develops an oil ring at the water line. This ring should be periodically cleaned using a non-abrasive tile cleaner or surface scum remover.
The other element of the skimmer that should be periodically checked for proper operation is the trap door at the mouth of the skimmer -- called a weir. The weir contains a buoyant material at the top that allows it to close-prohibiting debris from reentering the pool when the equipment is off or when there is lots of wave-making activity in the pool.
The weir is attached to either side of the skimmer housing with spring-loaded pins that fit into holes in the housing. Over time (and with a little horseplay) the pins may become disengaged, which prevents the weir from operating freely. Or, the ground shifts and the weir no longer has a uniform gap at the perimeter, which can cause it to stick.
If the weir is sticking, it can be removed and trimmed at one or both sides using a hacksaw to prevent it from rubbing against the housing. If the weir is not rubbing against the sides, but is on the sluggish side, remove the weir from the housing using a flat blade screwdriver to pry back the spring-loaded pins. Lubricate the pins and springs with Teflon lubricant and reinstall the weir.
If all else fails, replace the weir with a new one. Universal replacement weirs can be found at most stores that sell pool and spa supplies and can be installed in a matter of minutes using the removal technique discussed earlier. Also, skimmer baskets may, over time, develop holes or their handles often break, thus requiring replacement. You might be able to reattach the handle using a couple of zinc-coated screws. However, if the basket contains holes, it's a sign that the basket may soon disintegrate. Time to invest in a new basket.
If you hear your skimmer gulping water, the water level in the pool or spa is too low. Air is entering the system which can cause the pump to lose its prime. Always keep the water level at about midlevel of the waterline tile. In warm or windy months this may mean adding water almost daily. A pool cover can significantly cut down on water lost through evaporation.