HELP!

Hi ladies! I need some help here. I have the Chicco rim spout sippy cups for my son. They’re his special cups for his milk, his juice and water he gets in a regular gerber sippy cup. Anyway, for the life of me, I CANNOT clean the inside where the insert/valve goes into these cups. I can’t find anything small enough to fit in it! I always rinse them out as soon as he’s done with them, but somehow gunk got in there and I can’t get it out. I now have two useless cups because of this. If any mamas have these, please help! These are the cups.