I wouldn't try anything without Sotar's blessing but here is what works for me when I want to get out stains
1) citrus cleaner
2) goof off
I'd hate to have either damage your boat. Maybe Sotar will send you some material you can dip it in some cleaner for a half hour and see if it degrades. If nothing works, just tell your customer it was part of the Sotar color package ...
And in the future get your customers to wear diapers ...
Hey, if you want me to take a dump in a box and mark it "guaranteed", I will. I got spare time.