For the smooth production of filaments from polyesters it is very important to use accurately cleaned polymers and also accurately cleaned spinnerets. For removing remainders of polyesters from the spinneret a mixture consisting of at least 70 percent by weight of tri-, tetra-, penta- and hexaethyleneglycol and from 2 up to 10 percent by weight mono- and/or diethyleneglycol and up to 20 percent by weight of hepta-, octa- and higher ethyleneglycols has proved to give best results. Zinc acetate may be added for the solving process.