Here are my Fiends of Slaanesh before their bathtime ...
Dipped the models individually in the tub then let the excess drip off back into the tub, left an hour and removed all the surface paint. I then repeated the process but put the coated figures in a bowl overnight.
Next morning, armed with a toothbrush and bowl of hot water, I dropped them all in the water then scrubbed the paint away and they're nearly like new. There's no terrible smell like nail polish remover, which was my previous go-to, and did a better job too.
Here's how it looks when they're dry ...
It's £10 for a tub, but I've used maybe 10% of that cleaning down the first batch of old figures. Well worth the investment. The wife hasn't complained about an evil lingering odour, which is an additional bonus. In the dip at the moment are Blue Horrors, a Cauldron of Blood and then there'll be more models going the same way then up for sale.
If you want to have a look on eBay at my OOP pieces going for sale then click the link here.