These are products I have either tried or I think they are good to use. Remember, I am not a vet! So before you try anything, please consult your Vet.
Also, not every product is going to be a winner for every dog. I have some that can tolerate one food but not the other. I have had some that can tolerate the Liver treats but not others.
If you want to set up an in-kennel potty area, these are my recommendations.
Your puppies are already litterbox trained using these items (the litterbox is different but the items in the litterbox are the ones below).