If you're referring to the limber holes thru the stringers, etc that allow all compartment water to collect in bilge for bilge pump removal,
they are usually adequate size to ream out (gently to avoid gouging channel lining) with a screwdriver - maybe a Phillips -
or similar tool. Curvature of adjacent hull may make "angle" that prevents passing a long tool - then
bend a coat hanger or something similar to remove debris (often dropped screws, pieces of packaging, etc).
I doubt you can blow them out with air pressure if really blocked
Manufacturer usually can provide a diagram of locations, but you can feel them if out of sight or under bilge water
Hope this helps?