Use the appliance diagram rather than probing an unfamiliar opening. Air outlets, drainage channels, light housings and other fittings have different purposes and should not be treated as interchangeable cleaning points.
What the observation tells you
A small recess at the back of one model may look like the drain on another. Pushing a brush or wire into it could damage a fitting or force debris into a concealed area. Likewise, blocking an opening with food because it appears unused can alter the intended air path. The manufacturer's illustration identifies which areas the owner may clean and how.
A useful next step
Locate the full model reference and compare the drawing with the visible interior. Remove food temporarily only as needed and keep it appropriately chilled. If an opening cannot be identified with confidence, leave it alone and describe its position when seeking advice rather than experimenting with tools.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.