If manual, it can only be judged by the PH test paper. Simply speaking, when the cleaning liquid ( acid, alkali concentration) change little, because the distance between the CIP station and the pipeline of cleaning equipment is constant, the flow from the discharge pump is not change, so the time of every device being cleaned is almost same. If automatic, there is ion concentration detector (commonly used conductivity meter) on the cleaning road. It regards the ion concentration in clean water as standard, when the electric conductivity is lower than this standard, it indicates that the water washing qualified, CIP discharge pump stopping working.