How to clean the DPD-FAS "Chlorine Only" test tube?

DThompson55

Bronze Supporter
Jun 20, 2016
74
Manchester, CT
Over the years my DPD-FAS "Chlorine Only" test tube has stained badly above the 10ml line, possibly DPD or FAS or some byproduct, above the 10ml line. Is there some solvent or something that might remove it and get it back to close to new looking?