Linear rail greasing tool

I tried to grese linear rails based on this NERO 3D's video https://www.youtube.com/watch?v=UYvhYjkBFTY but hated how you end up with the grease all over you hands.

So I designed this simple adapter to help.

Printed using PETG (does not really matter), 0.2 layer height. Then lightly sanded the edges to get better seal.