Hydraulic fluid straight from the drum, has a typical cleanliness level of ISO 4406 21/18. A 25 GPM pump operating continuously in hydraulic oil at this cleanliness level will circulate 3,500 pounds of dirt to the hydraulic system's components each year! To add hydraulic oil, and not the dirt, always filter new oil prior to use in a hydraulic system. This can be accomplished by pumping the oil into the hydraulic reservoir through the system's return filter. The easiest way to do this is to install a tee in the return line and attach a quick-connector to the branch of this tee. Attach the other half of the quick-connector to the discharge hose of a drum pump. When hydraulic oil needs to be added to the reservoir, the drum pump is coupled to the return line and the oil is pumped into the reservoir through the return filter. As well as filtering the oil, spills are avoided and the ingress of external contamination is prevented. The benefits of carrying out this simple modification are well worth the minor cost involved.