Sounds like a SPC exercise. Does the cleaning include types of materials used (e.g., lint free rags), flow rates w/a specific nozzle size, dimensional properties of the joint including tolerances and variations, etc.? It appears what you want is to identify the cause or source of discontinuities and not key characteristics of the process.
Fine pores in Al are common, what does your AC require?
Is your client trying to completely remove all porosity?