Iuse liners, which get ditched in the rubbish after every change so there were no really pooey ones, and my bucket has a lid, it's the same bucket I've had since Maya was born from the good ole Warewhare,a proper lidded nappy bucket. I have no idea how they got in the bucket, will have to make sure that the nanny is putting them straight in the bucket after every change and not leaving them sitting around at all.
The funny thing is we have a Robocan so there are usually bugger-all flies in the house. I am still grossed out by the whole thing