It isn't so difficult to toilet-train a slave:
1. One night, let him out of his cage and have him sleep in bed with you. Tell him to rim you. Make sure your ass is clean and odor-free the first time. If he balks, you could promise him a reward in exchange, like a blowjob or letting him in your back door. Continue to ask him to rim you regularly.
2. Gradually reduce the rewards.
3. Start to ask him to rim you when you are not clean, like just after you've had a bowel movement. Do this regularly, but still wipe like you'd normally do--don't yet actually ask him to clean your anus with his tongue yet.
4. When he gets used to this, it is time to get him to start consuming actual waste. Start with piss, not shit. One night, tell him you need to pee and you don't feel like walking all the way to the bathroom. Have a plastic shower curtain liner handy. Put it down on the floor and tell him to lie on his back on it. Sit on his face, with your clit directly over his mouth, facing his feet, and pee in his mouth. Make sure you are sitting heavy with your full weight on his face so that no pee squirts out and makes a mess. Do it in short squirts so that he can keep up with it and swallow. Give him a hand job while you pee so that he associates your piss in his mouth with pleasure (Can you say "Pavlov?"). Try to time it so that he climaxes just after you finish peeing. He might puke up afterward or dribble some, but that's what the plastic is for. And he still needs to learn to hold his breath for long periods of time, but that will come later.
5. Gradually increase it to two times a night--drink plenty of water before bed so that you will need to pee a few times during the night.
6. Eventually, you will decide that he will be your toilet every time you need to pee.
7. At this point, gradually increase the duration that you make him hold his breath. Use an egg timer or something similar--but don't let him see you doing this. At first, you want to make him hold his breath for no more than about 10 seconds at a time. Every day or two, increase his time between breaths by about 5 seconds. Eventually, you'll want him to be able to hold his breath for 3 to 4 minutes--an eternity for someone not accustomed to holding his breath for very long. If you sit and make him hold his breath for 4 minutes the very first time, he'll likely pass out. Passing out from holding your breath can be dangerous, so it's something you want to avoid happening--although he probably will pass out every so often, even after he has learned to hold his breath for long periods of time.
8. When you get him to where he can hold his breath for about 1 minute while you pee, it is time to move to shit. You are continuing to have him rim you regularly after you shit, right?
9. Start by telling him to rim you after you've taken a dump without having wiped. Tell him to lick you clean. Do this a few times.
10. After he has accepted cleaning your ass after you shit, it is time for him to become a full toilet. To shit, sit on his face facing away from his feet with your anus over his mouth, and let your bowels move into his open mouth. Your weight on his jaw will prevent him from being able to close his mouth.
11. Again, don't make him hold his breath longer than he has become able to. By this time, he should be able to hold his breath for about a minute, so you can excrete a couple of stools into his mouth before lifting up to let him take a breath and swallow.
12. From this moment on, he should become your full toilet at home every time you need to pee or shit. Continue increasing the time he holds his breath by a few seconds until he can hold his breath for about 4 minutes. Longer than 4 minutes is dangerous.
13. Be aware that many shopping malls and other public places have private "family" unisex restrooms. This provides opportunities to use your toilet slave, instead of some filthy public toilet seat, while you're out.
14. At this point, there is no reason why you can't dispose of other bodily gunk into his mouth too, like finger and toenail clippings, bellybutton lint, snot, etc. And don't forget to have him lick you clean regularly during your period.
Congratulations! Your slave has been fully toilet trained!