The invention provides a method of adding solvent or make-up fluid into the gutter line of a continuous ink printer. During the addition of solvent, the vacuum level in the gutter line is monitored and maintained at a level sufficient to ensure that vacuum is maintained at the gutter. Vacuum level in the gutter line is preferably controlled by controlling the speed of a variable speed gutter pump. Noise in the gutter line is preferably used as a control over pump speed.