Helle - I don't, lol. Second hand ones I will, but new ones go straight on the butt to see how they look
I used to make sure I did the 3 hot washes of bamboo etc first, but I don't worry now. I know (from making my own) that all fabrics are washed before nappies are made, especially bamboo to help with the shrinkage. I hot wash my bamboo & dry in the dryer to get max shrinkage done before I use it to sew.

WOSB - pocket change