Oil, NEVER throw away this part of the cap: it’s very important, that’s exactly what it’s used to.

You must put the small piece you removed into the oil bottle.
As already mentioned, the small piece you have removed from the cap should be put back in the bottle. Before putting it on, take the ring between your forefinger and thumb, press lightly and place the ring first at the bottom of the oil bottle.

As you can see on the bottle, there is an opening inside, where you have to pass the ring. The opening is quite large and is surrounded by many plastic parts arranged in a radial pattern. If the bottle is used as such, the oil comes out in large quantities.