Hi. So sorry to hear about your dog. My JJ also has bladder cancer. He wanted to go out really often until we got him started on Piroxicam & antibiotics, and the meds seemed to ease the irritation in his bladder that was making him need to go so often. Within a couple days of starting meds he went from wanting out every 15 minutes to being fine for up to 3 or 4 hours. He also wears a diaper so if he leaks in between outings he's not distressed by getting pee on the floor. Hope this info helps you. I haven't tried the graviola so can't help you there.
Joy & JJ.