I would love to know this as well! The stupid squirt toys have mould on the inside which I can't get out and they all keep getting slimy and mouldy. They are all in a mesh bag out of the water so I don't know why.

I have in the past soaked them in a bleach solution and then rinse/repeat with clean water and a tooth brush to make sure the bleach was all gone. Getting very close to throwing them all out and buying something else (except DD loves them)