As a fibre artist I buy a lot of used clothing at garage and church sales, thrift stores: the price allows for guilt-free cutting a garment back to a former state of cloth (the original state is likely a sheep or a plant) and taking part in the adventure of recycling.
What I have found over the years is that, when I immerse the item in water (to which I have added a drop of disinfectant) the water may become a bit soapy. Not sure if this means too much detergent has been used and marched through the rinse cycle. It’s always a bit startling of a discovery and makes me more aware of how much soap I use when I machine wash. I don’t want to be wearing or sleeping on or toweling with a cleaning product!