Are you making the water deep enough? I've noticed that Lizzy poops at the deep end of the tub by the drain, and I think it is because the water is deeper there and maybe gets not only his belly but also his sides warm and then nature takes over. I've heard it should be shoulder deep on them. Lizzy definitely likes his water warm. In fact, I take my shower first so my shower gets the bottom of the tub warm and then he gets his shower while the tub is still warm. Hope this helps. I have him on a schedule also. He wakes up 45 min before me, I get up, he eats, I get a shower and then he gets his shower. It works like a charm. Maybe the timing is important. Once you get the cycle going, dont break it. I change his lights so that they come on and we start our routine later on the weekends, but the routine is still the same, withthe intervals the same.
Honestly, once you get him going in the tub, it is the greatest thing! He was easier to train than my dog. And he NEVER poops in the viv! I love the guy!