@myello, first off I am surprised at that recommendation from the manufacturer. Generally the piston in a spring gun (remember, your Nitro Piston is a spring gun using a gas strut filled with Nitrogen as the spring) only needs a very little silicone oil like RMCOIL maybe once every 6-8 months when the gun is shot regularly each week. Modern piston seals are made of synthetic material and do not "soak up" the oil the way older leather seals had to in order to remain pliable. Your Nitro Piston gun, like my own, only needs enough RMCOIL to prevent the piston from gripping the inner air chamber walls - a situation easily recognized by the "honk" sound the gun makes when it is being cocked or even shot. With the long-lasting stability of silicone oil you need only to put a drop into the chamber often enough to maintain a thin sheen of oil on the inner walls. As I said, for me that's been no more often than a drop every 6 months or so, and I shoot my springers 4-5 days a week for at least an hour. You want to break open the breach and load a pellet, hold the rifle so the stock and air chamber are vertical with the breach at the topmost end, and while still cocked open and exposing the air port (hole) at the end of the air chamber squeeze a drop of oil directly down into the air chamber. Two drops won't be a problem but any more than that and you're just wasting oil that'll blow out through the air port and down the barrel as you shoot. The oil you drip into the chamber will rapidly be dispersed throughout the chamber to provide the lubrication you want. I say load the gun because I've tried lubing the chamber without fully cocking the gun and it is a pain - and much riskier in regards to having the barrel slip out of your grasp and slam shut! Just have a pellet trap or trash can filled with newspaper/cardboard bits/old rags and fire the pellet into that trap. Then go about the business of shooting.