I chuck wet-only nappies straight in the machine and keep the door shut; they get filtered thru with the ordinary washing.
Doesn't help with poo-ey ones, I realise, but does lower the number of smelly items. The poo-ey ones need washing at 60 anyway, and can be filtered thru with bedding or anything sicked up on.
Another idea: Keep the nappy bucket in a cold room, instead.