Review on CPS Products TLJ4 R134a Oil and Dye Injector: A Must-Have for Effortless Refrigerant Maintenance and Leak Detection! by Ray Sheptock

A little tricky to use (suction system, suction oil and then suction again - follow instructions provided) but works great. Very good construction. Securely hold pressure with o-rings and a ball valve on the bottom. One end connects to the manifold gauge set and the other end connects to the low pressure hose. One note - his time frame of how long it takes for the oil to be absorbed was very different for me - I had to quadruple the time frame (used with ISO 150 PAG oil - to make it thick). I continued sucking (as instructed) until the vacuum pump sound changed (which let me know all the oil had been sucked into the A/C system.