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 BM, 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)
I will have a to take a closer look at my penis. I must have gotten stretch marks from all the LengthMaster - Penis Bundle Stretcher & Weight Hanging bundled exercises that I've been doing. Not bothered about it though.