Whatsup fella's. I'm a in a "in house" HVAC-R dept. at a steel mill. Anyway, I'm still new to the field. Anyone with less than 3 yrs exp. is new actually. Well, today I was pulling a vacuum on a unit and all seemed fine. Vacuum held passed 30. I'm ready to charge. I takeoff the yellow hose from the pump and install it on the R-22 tank. As I open the tank, I go to purge the line and oil started to spit out. . I don't think oil got into the system because I closed the manifolds before I stopped the vacuum. But where did the oil come from, and why? Any help woould be great.