A catch basin is a part of a storm drain or sewer system which is designed to trap debris so that it cannot enter the drainage pipes. Catch basins are a large scale version of the traps used in home drains to accomplish a similar function. Most municipal sewer and storm drainage systems use catch basins, and the design is basically the same all over the world, with a few small variations. Typically, public works agencies maintain storm drains and catch basins, although individual citizens would be well-advised to keep an eye on local storm drains so that they can report problems promptly.

Catch basins have a wide sloping inlet which collects runoff, assuring that even when high volumes of water are being dumped into the system, there is minimal overflow. The inlet opens to a pipe which is covered with a grating. The grating traps large debris, preventing it from entering the piping. As water floods the catch basin, small particles which slip through the grate settle to the bottom. Drainage pipes are located above the bottom of this vertical pipe, ensuring that the water which flows into the drains is clear of sediment.

Maintenance of a catch basin includes regularly clearing the grating of debris so that the drainage is not inhibited, and periodically cleaning out the trap at the bottom. If particulates are allowed to rise high enough, they can start spilling over into the drains, which can become an issue. Many cities clean storm drains regularly, and pull out sediment after the rainy season.

In some cases, the catch basin may be designed in such a way that it prevents backflow of gases from the pipes. This is common with catch basins in sewer systems, so that the distinctive odor of the gases which build up in sewers does not rise to the surface, where it could irritate passerby. The catch basin may also include features which are meant to deter rats, as rats can be a common problem in drainage and sewer systems.

It is also possible to use a catch basin in a home drainage system, although the scale is usually smaller than that of a storm drain. Many plumbers are qualified to put in catch basins, and they can also provide a quick overview of maintenance techniques to ensure that the catch basin remains effective.