First thing is to put them in the wash with your other nappies .. after drying they will be ready to use. However, the full absorbency of the fabric will be experienced after 3-4 washes. The nappy fabric was pre-washed, but will find the nappy will shrink a little too.
A lanolised soaker is best for over night nappies, as it is completely breathable and waterproof - not to mention gorgeous! Wool can hold up to 4O% of it's own weight in fluid before it feels wet.
When boosting night nappies, the extra layers are best added to the outside of the nappy, in between the nappy and cover. Otherwise leg gapes may cause leakage.
If you can, wait until bub has fallen asleep before changing her/him into the sandy. Just so that last wee for the day is in the nappy bucket. If baby is still feeding a lot through the night you may find you need to change it during the night. How many wees a sandy can hold depends on a few things. But lets just say that I know they can hold an older toddler heavy-wetter wee first thing in the morning - now that says something!!