This is a very simple fix, my man.
Use 2-part household epoxy glue, which is available at any convenience store, to permanently bond the tube to the nipple. Use a very small amount on the tip of the nipple otherwise, after you slide the tube into place the excess will drip and need to be cleaned up.
You could use super glue but the brittle nature of the crystalline structure is not ideal with the flexible silicone tube. I have tested “gorilla brand” which is nice because it is thicker and slower to dry, but epoxy is ideal. We would do this for you at the factory but then it would not be possible to remove the tube for shortening which is an important option to have.
Actually, the super glue might be a way for us to temporarily secure the tube in place which would allow for removal of the tube without destroying the nipple. If removing the tube to cut shorter is required, the 2-part epoxy can be used for a permanent bond.
I will test this and see if it is suitable as a temporary bond which can be removed by force without causing damage.