I didnt want to name anything- as we may have different products out here. But what I use is a spray called Cetrigen. Its an antibacterial with active ingreients Cetrimide, diethyl toluamide and di-n-propyl isocinchomeronate. It is purple and also contains an insect replent to stop blow fly strike.. Its fairly geeneric as far as what animals you can use it on- poultry , horses, pigs, cattle.
I cant use it straight out of the aerosol is it would colour the whole duckling purple. I spray some into a small container and paint it onto the navel area with a cotton bud.
I also make sure bedding is cleaned more often to eliminate moisture or dampness.