Filter grind should do you; given the nature of the machine I'd have thought it would be worth using decent but not posh coffee IYSWIM. I'd guess most of these machines see supermarket gold blend at best (I'm a vicar's kid, and have made a lot of church hall coffee in my time...)
Great, thanks for that. Hopefully that's what this one is too.
What kind of grind would I need for it?