This. Please don't reuse them. They're foam. I don't care how clean or how solid they look or feel, foam is incredibly porous. Pores mean there's wonderful places for bacteria and mold to hide from soap and water. Not even soaking them in something nasty is gonna fully sterilize them to a level I'd be comfortable with placing into my body.

Grab some reusable concert or regular earplugs. They're a million times easier to clean, safer for long term use (you're not meant to wear the foam ones longer than a couple hours), and you'll skip on a lot of infections.