In connection with an automated peptide synthesizer, an apparatus and associated method through which peptides produced in simultaneous multiple synthesis are together isolable. Cleavage to liberate the peptides from linkage to the support matrix of the solid phase is carried out in the same vessels in which the synthesizing reactions took place. Prior to cleavage, a drainage port of each reaction vessel is closed off by a cap. The reaction vessel is inserted into a centrifuge tube, which in turn is put into a rack supporting a number of tubes equal to the number of channels of the peptide synthesizing apparatus. After the peptides are cleaved and dissolved into cleaving solution added into each of the reaction vessels, the caps are removed from the drainage ports of each reaction vessel, and the vessel is returned into the centrifuge tube. A plastic jet-fitting attached to the nozzle tip of a blow unit pressure gun is inserted into and pressed into contact against the supply opening of the reaction vessel. Operating a trigger of the pressure gun releases pressurized inert gas into the reaction chamber. The peptide-dissolved cleaving solution is thereby passed through the drainage port, and is thus transferred in liquid phase into the centrifuge tube as filtrate. Associated with the blow unit pressure gun, a needle tube fitting is provided for localized desiccation of wetted peptide following precipitation and centrifuging.