I was chucking them when they got gross too. I tried filling them with a bleach solution and then rinsing ++++ but that was too hard for the bath toys IYKWIM?
Gluing the hole shut is a great idea.

We have dinosaurs, sea creatures, washing powder scoops, plastic spoons, a jug, a couple of medicine eye droppers, a couple of Barbies.....


and yep...but the rest of us are here too.