Cleaning bath toys?

My son has a bunch of bath toys that get water inside them. Some are designed as “squirters” and others just have a hole in them. I always try to get all the water out, but of course it’s impossible. Now I’ve seen black gunk come out of some of them, and the lighter colored ones I can see have patches inside. And, of course, he constantly puts them in his mouth. 🤢

Any suggestions for a safe, effective and relatively easy way to clean inside them or do I just need to throw them out?