How do I Identify storm drains vs. sewer drains outside?

 If it's a drain (ie it's designed to capture surface water than it is by definition storm. a catch basin is just a basin of any size used to capture sediment and debris and keep it from cloggin up a drainage system - if theres a grate then it's storm. Mahole covers are typically solid or mostly solid as opposed to storm which have a good number of holes or are grate like. Also it's important to point out that a number of cities will not have two separate systems. Difference between a storm drain and a catch basin - well a catch basin is merely part of a storm drain - it's the part that's designed to keep the rest of the system clear of sediment and such by capturing it in an accessible basin which is easy to clean out.