Diff draining

To drain the oil from the diff' you either: suck it out with some sort of syringe or electric gizmo OR remove the back plate [ messy].

The latter has the advantage that you can give the innards a visual check and possibly a clean prior to refitting and refilling.

Question: How hard would it be to drill and fit a suitable drain plug to the diff'?

Why you need a drain plug, oil does not change it so often and it is not a hard job, you need a key and silicone seal and a bit of skill

True, thank you Tony.