I've switched to using a nappy bucket liner inside the bucket to contain the smell. It's waterproof and washable. So it can go in the wash with the nappies. Also means I don't have to get my hands in there any more to load a bucket of nappies into our front-loader, which was a disgusting job for sure.

Yay for no more horribly smelly buckets! And I don't have to disinfect the bucket all the time now, either.