The solid retention in the bucket is essentially influenced by the entry of organic matter in the form of leaves, tree branches and other bulky objects.

When a catch basin (CB) does not hold organic matter in its bucket, there is practically no solid retention, because the mineral solids with particle sizes of < 16 mm (0.63 in) pass through the slit openings with the slightest volumetric flow.

Consequently, catch basins with an outlet at the invert level are generally inappropriate for the retention of solids in intra-urban areas where a higher percentage of mineral solids is present on the roads.