LOL LOL Gotta love those stool samples. Following him to the 'restroom' would be a good way to distinguish which poopie is his if all 3 share the same litter box. Alternatively, you could always put him in a separate room with his own box for a few hours or something and go and collect it from there. However, fresh poopie is the best, and you can keep it fresh by putting it in the refrigerator if the vet visit is several hours or even a day from when you collected the poopie! LOL