Washing bigfoots?

Hey squish squad! So I've been a collector of bigfoots for about 3 years and as gross as I feel admitting this...im terrified to wash any of them in case they get damaged!!! But my older ones are becoming a lil discoloured so I figured it's high time I did. Should I just put them in a pillow case in the machine or is it a soak in the bath and airdry situation?