Yep you can squeeze them out to clean them.
Mine have got some brown spots on them, from where food has landed on it, and my fish has "ummed and ahhed" about whether to eat it or not.
I take mine out every so often for 1-2 days in clean water, and put them in a jar somewhere sunny, as I realised they weren't getting enough light.
When you first put them into your tank, they may float, you can weigh them down with a stone, or just let them sink naturally. My fish loves 'nudging' them and darting off when they're floating!