Nickel, nappisan ruins elastic and PUL, so steer clear of it for MCN. You can make a napisan paste and layer it on the stain and leave it for a while before rinsing it in the sink.

My best remedy for stains is to use Sard wonder soap on the stain in the laundry tub or under the water going into the washing machine (top loader). Rub it together with some sard soap like you do any other stain and it comes good. J does the worst stains and this is keeping my itti d'lish's nice and white inners LOL.