I can recommend le Paradis at St Leon-sur-Vezere. It's a beautiful site with very friendly owners. Excellent and very clean facilities with childrens' washing areas.
James, we stayed at Les Deux valleys near Vezac a couple of years ago. It is run by a very nice Dutch family and can become a bit like little Holland in July / August but overall very good.
It would be very difficult to find a campsite that doesn't have CLEAN facilities these days. Not so thirty years ago when I first caravanned in France. I sometimes then stopped on a site called 'Camping Clean Toilets' which was to the south of Souillac.