Not all syrians will take sand baths of their own accord, so it may be that if you offer a sand bath to Herman he will always use it as a litter tray [which is fine and natural behaviour, its always nice to provide your ham with different safe and natural substrates]. If you want to you can try providing two sand baths as some hamsters like to have one to use as a bath and another to pee in, or when you handle Herman you could sprinkle a tiny bit of sand on his back and gently comb it through, I do this occasionally with my long haired male to keep his coat looking nice and he doesn't seem to mind at all.
I would say don't fret about him using the sand as a toilet, it just makes spot cleaning easier! I would recommend letting have access to a sand bath or two in his enclosure and let him decide how he uses them
