Draper - AdBlue Tester (Disc Type) Accurately measures the strength of urea concentration in DEF (Diesel Exhaust Fluid)/AdBlue solution. Easy to use AdBlue tester, simply squeeze the bulb of the syphon tube and insert the tube into the DEF / AdBlue solution. Then slowly release the bulb and draw off enough liquid to reach the line marked on the tube. The number of floating discs indicate the urea concentration. Once used wash and flush the tester with water. For testing, at hot or cold temperatures the 740mm extra long hose is designed for tanks with filler necks.