Drug dissolution testers, particularly the most commonly recommended ones (paddle and basket), are based on a closed system/environment, i.e., without a drain. Therefore, it is not possible to have or create a sink condition. Yet, authorities and pharmacopeias require it while “experts” create it. How? Magic!
In addition, one does not require a sink condition for in vitro drug dissolution testing. 900 ml of water with or without a small amount of solubilizer sufficient to (freely) dissolve the expected amount of drug present in the product – is all one needs. For further details, please follow the link to simplify your life and avoid wasting time and resources (link).