@GraemeE
put it in a gallon ziplock bag, run some water in, put a tiny dab of whatever soap/detergent you want, zip it tight with a little air inside, and shake the hell out it.
pop the zip open a little, pour the dirty water out, run some clean water in, zip it back up and shake the hell out of it, rinse and repeat until the water being drained is running clean
that’s what I’ve done with my hats in the past, it’s easy as all get out and works fine for me


