I consider stretch-marks, discoloration, etc. as 'war wounds' and 'badges of courage'...a testament to all my hard work.
If you have a bottle-brush, that will help scrub the insides of your [words=https://officialhydromaxpump.com/?uid=6&oid=2&affid=98 ]BM[/words], but there's really no way to fully clean the valve...so perhaps look into removing the entire assemble and replace it w/the VacuVin winemod (more powerful too)