5.3 Periods without operation If the capillary viscometers are not used over a long period of time, the liquids contained in the system, in particular aggressive solutions, have to be drained. If the liquid is left in the system, one has toreckon that the solutions used will alter in the course of time and attack the glass, in particular the capillaries.Cleaning agents should be matched to the previous samples or impurities! In many cases, an aqueous cleaning agent (glass cleaners, detergents) or organic solvents (such as acetone or hydrocarbons) are sufficient.