I decided to search Sprite's cage to find any wet bedding. I put him in his playpen and my partner supervised him. It took me an hour to take everything out and hunt through the bedding and I found, clean little Sprite only toilets in his sand! Poor Sprite was not happy being in his playpen for an hour and he actually managed to escape. Luckily my partner was watching him and he quickly caught him.
I feel pretty bad to uproot all Sprites lovely tunnels but at least I now know all I have to do is carry on sieving his sand and I can leave his bedding untouched.