Draper-97983-Ad Blue-Tester-Disc-Type-Draper-97983-Accurately-measures-the-strength-of-urea-concentration-in-DEF-Diesel-Exhaust-Fluid-Ad Blue-174-solution-Easy-to-use-Ad Blue-174-tester-simply-squeeze-the-bulb-of-the-syphon-tube-&-insert-the-tube-into-the-DEF-Ad Blue-174-solution-Then-slowly-release-the-bulb-&-draw-off-enough-liquid-to-reach-the-line-marked-on-the-tube-The-number-of-floating-discs-indicate-the-urea-concentration-Once-used-wash-&-flush-the-tester-with-water