CMD (npub1ecj…fchy) honestly, I'd want him out of the house to, not because he masturbates, but as a preventative for something like that happening again. It's not just a potential health risk, it's just downright disrespectful to your parents.
How would you like your dad to regularly relieve himself in your backpack? After all, he febreezes it after each use. How'd you like your mom to to use the pages of your diary as toilet paper. she'll replace the stolen paper. it's a matter of common courtesy
Doing this the first several dozen times as a young tween who doesn't know better is forgivable. but it shouldn't take you long to develop a sense that this is kinda messed up and you should find a better way to do this.