The invention is a method that allows contamination-free transfer of a liquid from one container to another and devices including embodiments of a transfer apparatus and adaptors that are used to carry out the method. By contamination-free transfer of liquid it is meant that during the transfer process there is no leakage of the liquid or air contaminated by the liquid or vapors of the liquid to the surroundings and also that no contaminants from the surroundings come into contact with the liquid. The main advantages of the method, in addition to its simplicity, is that at no stage of the transfer procedure is there leakage of the liquid or air contaminated by the liquid or vapors of the liquid to the surroundings and also that no contaminants from the surroundings come into contact with the liquid. The present invention is particularly directed towards providing an apparatus that is adapted to effect contamination-free transfer of a hazardous drug to and from any container equipped with a standard connector port.