For PUL wraps the easiset way of stripping I have found is the dishwasher tablet method. Am quoting all the advice we give out just in case :
"Always start with clean nappies. First run a maintenance wash on your machine to clean it too (empty machine, full dose of detergent and the hottest wash you can. Don't forget to clean the detergent drawer out) to make sure there is no build up in pipes / your machine that will affect your strip wash.
Washing-up Liquid Method. Soak your nappies over night in a bath full of water and lots of washing up liquid. If they really smell bad, you have nappy cream build up on them, or you are just a glutton for punishment then next morning you can scrub inserts / nappies with a nailbrush with neat washing-up liquid on it. Drain it all off and then bung in washing machine and keep running rinse cycle until you see no more bubbles from the liquid. Suitable for all types of nappy and good at shifting stains.
White Vinegar method: Soak your nappies overnight in a solution of water and white vinegar (1/8th - ¼ vinegar depending on how bad the nappies are) then drain and do a couple of rinses in the washing machine until vinegar smell is gone. Not suitable for PUL, bamboo or nappies with elastic.
Dishwasher tablet method: Use alongside the white vinegar method. Stick all PUL or elastic containing items in the washing machine with a dishwasher tablet. Run on a 60c wash (so only use on wraps etc that can be washed that hot). Run an extra rinse cycle to ensure all gone. Not sure about suitability for bamboo items so wouldn't risk it with them"
White vinegar is only really recommended for terry type nappies. Cold rinsing works, but can take forever, so if you can get away with it the dishwasher one is fab. Depends on how hard your water is though, and how bad your build up.
Lots use gel liquids to wash now, but allegedly they are bad at leaving residue on the pipes etc of your machine. So even if you use a small amount your nappies are probably picking up additional from the machine, maybe even softner too. Is worth doing a service wash (hottest you can, either empty or with one of the washing machine cleaner you can pick up at supermarket) on your machine every so often to - prolongs its life too.
HTH