In England we fly a lot of diesels. Silicon fuel tube is no good for this. We use a transparent plastic tube, and I have used a large bore bit of this, forced over the end of the O.K. needle and left as long as necessary. I used this on my O.K. 0.149 Perky.
You could plug the end with a bit of balsa or dowel of suitable size, to give it some "body", but I never needed this.