As far as the question on "How to calculate flushing quantity of equipment..." I would say that you need to take into consideration primarily the solubility of both the solvent and cleaning agent or detergent you're using as well as the cleaning methodology and design of equipment, to make a scientifically based and quantitative calculation of cleaning or flushing volume.

In respect to the calculation beyond solubility and as it relates to equipment design, you need to take into account things like contact surface area, crevices and hard to reach areas and how these areas will be cleaned in order to ensure sufficient flush or rinse volumes.

Once this quantity and methodology of cleaning is defined, it should be followed by testing of rinse and swab samples to confirm residual drug and detergent or cleaning agent removal. Once confirmation is completed, the cleaning procedures should be specific enough to ensure that the cleaning methodology including rinse time and volumes are sufficient enough to ensure cleaning repeatability post validation.