Drop Inlets

A standard concrete drop inlet (a form of a catch basin) is a below-ground square box precast concrete structure with a horizontal square opening.

Typically, a slotted or perforated metal grate is set into the top of the drop inlet to bring it to ground level to allow water to enter into the structure.

During a heavy rain storm, water drains from the surface area into the grate openings of the drop inlet. The water then drains into a stormwater pipe that is connected to the drop inlet. Many catch basins can be linked with pipe to create a network of drainage points. The water moves to its destination through the system of pipes, using gravity.

Concrete Drop Inlets - A Cost-Effective Solution

Drop inlets are a cost-effective alternative option to custom-made catch basins. A major advantage of a drop inlet is that an installer can make as-needed on-site adjustments to it. For example, holes must be made at certain elevations of the drop inlet, to accommodate certain size pipes. If a contractor ordered a custom-made catch basin and the project specifications changed (hole elevation, hole size, hole orientation), the custom structure would be useless and a new one is needed.

Precast concrete drop inlets manufactured by A.J. Foss are AASHTO HS20-44 Traffic-Rated.

View A.J. Foss Plan & Elevation Views of a Drop Inlet

Drop Inlet Uses and Applications

  • Storm Water Management
  • Traffic Rated-Roadways & Parking Lots
  • Non-Traffic Rated-Pedestrian Areas


A partially recessed shape is cast-In to the concrete during the casting process, leaving a wall that can be broken on site to create the desired opening shape or size. Oval knock-outs are offered in multiple locations to provide access for pipes required. Hole size and locations can vary, and knock-outs are easily broken with a hammer to create desired opening shape and size. Up to 15-inch pipe can be used with drop inlet knockouts.


A shaped opening is cast-In to the concrete during the casting process, leaving a hole-specific access opening for Pipe or Box Culvert. Round cast-in openings are offered in multiple locations to provide access for pipes, and opening sizes and locations can vary. Rubber boots can be used with this option.

Contact us to discuss your projects throughout New Hampshire, Maine and Northern Massachusetts that require wastewater and stormwater products, and discover the A.J. Foss difference for yourself.

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