Awhile back, we noticed that our sippy cups were stinky. We always air dry them, and used to store them with the lids on, but stopped doing that, thinking that water was getting trapped inside and that was what was making them stink.
Last night I was putting away some cups, and noticed something black in the hole in one of the spouts. I figured it was food from the dishwasher, so I tried to get it out with a toothpick. I realized it wasn't coming out so I pulled out the valve thing. It was FULL of black mold. I was so grossed out. I know Holly used this cup within the past week or so, and I am just sick to think she was drinking that. We typically only use sippies when we're out and about since we're trying ot have Holly use an open cup at home. So who knows how long it's been like that, or how long it's been sitting there with mold in it.
I pulled out all of her cups and none of them were as bad as that one, but some had water trapped between the valvue and the spout, and some smelled bad. I took them all apart, soaked them in vinegar, then boiling water, then sat out to air dry, disassembled. I think we'll probably stick to the take & toss ones or other ones without spill-proof valves from now on because I just can't handle the idea of my kid drinking mold.
Anyone else dealt with this? Just thought I'd post it as a PSA, if nothing else. :-(

Re: Ugh.. mold in sippy cup spout
It is easy to happen, we have dissassembled them each time they go in the dishwasher to make sure nothing grows in there. Then I guess the heat dries them in the DW.
I havent had a problem with them doing that. We use the straw sippies so I know its a few more parts but it works. Good for you with the open cup....I just cant do it yet. I dont want the mess.
THIS. We had that problem at the very first, then since I've always had to take them apart. they go through the dishwasher taken apart after each day.
***Baby #3: BFP Mother