Thanks for the replies.
The tubing is approx. 6mm in diameter and 80mm long. It's a clear, soft pvc tube.
I've spent ages trying to find it. Looking through the filler hole with a mirror and torch, but to no avail. I don't think there's enough space for the tube to find it's way to the drain hole. Can't poke my grabber up, as there's something right above the drain hole, limiting access.
I had plans for a nice productive day off today. Had already changed the diff oil, sorted a rattling heat sheild. It as all going well and then this happened