A method of cleaning and flushing a fast-set material spray gun 10 is disclosed which uses, in the preferred embodiment, a mixture of approximately 62.5% DMSO, 32.5% DBE and 5% water. This mixture 12 is non-toxic when atomized and lowers the freezing point of the liquid to below 10° F. Because the solvent is mixed with the purge air and expelled from the gun in atomized form, it is important that a non-toxic solvent be utilized and also important that the freezing point of the mixture be low enough to allow use in colder climates without freezing.