Personally, I have never used either pee-pads OR litter boxes. Except the one time, and I found I had litter all over the place, not in the box and the pups would use it once, one pup, and the rest would say 'yuck ! not going THERE ! its dirty !' So I gave it up within a couple of days.
My pups were always semi potty trained before they left me - so new owners had them totally clean within a week or so.
OUT ! immediately after food, sleep, playtime. No if, no buts. And back in when you have been clean doggie. Lots of praise and they catch on very soon.
At many of our indoor shows in this country, there are several areas, roped off, with sawdust quite thick on the ground. The intention is that your dog, whatever breed, relieves him/herself in this patch. They are euphemistically called Exercise Areas.
NOT for Basenjis ! I have had them hold it for hours rather than set foot in the filthy sawdust. They really hated it and would NOT use it, which is why I'm surprised they would use litter.
One year at Crufts, Plessy was desperate, we were not allowed to leave until 5 and it was about 3 minutes to. I begged the little Hitler on the door to let me take her outside, but no. So my little angel unleashed the floodgates - all over his shoes !
Lavish praise from Mom !!