I've tried everything - using very little detergent; cold wash first with no detergent, etc. - but I cannot get the pee smell out of my Bumgenius nappies, particularly the outer layer. I use a hemp booster with the Bumgenius microfibre one, and funnily enough - even though they're the bit that absorbs most of the pee - the hemp ones come out smelling fine. The microfibre boosters come out pretty much ok (though not completely fresh) and then, as I say, it's the waterproof outer which I just can't get to smell clean. I've been using them for about 18 months.
Any top tips? Thanks!