RTE-PEN - New Stay-Clean Flux Pen. Filled with original Stay-Clean acid flux, the pen has high quality bristles and a spill tight cap. 1) Before first use, twist the non brush side of the pen, it can only go one direction, until the air bubbles are gone and it begins to dispense flux. 2) Once the flux begins to dispense for the first time wipe it on a paper towel to insure there wont be too much excess. 3) Each additional use only requires a few twists of the cap and light pressure to control flux usage