All drop down lists require that you specify a value list.
No need for an extra table or table occurrence if you want the existing values in your value list to be the source of values for you drop down. Just define a value list and specify that the values come from this same table and field in the value list set up.
Thanks for that! I said I had a mental block, I have no idea why I didn't try that. I've still got database culture shock, obviously!