Oh yes - why do they make those toys:) We have tons of them. I only let them play with a few at a time for a few weeks and then I throw them away and then put new ones in the tub. We are always in constant supply with Birthdays and holidays.
I guess if you really wanted to save them, I would try to use those little infant syringe medicine droppers and try to stick the tip in the hole and squirt in antibacterial dish soap or something like that.
The other thing to do is sqeeze the toy flat and then release it in a bowl of soapy water so it sucks it up. Then shake it around and squeeze it out.
You still might have to throw it away though if the black stuff doesn't come out. That's just too much work for me though, so I just throw them away:)