using silent water bottle

so i got an All living things quick fill bottle http://www.petsmart.com/product/inde...AvailInUS%2FNo here is a picture. For those who don't know how it's made, the valve has a metal wire sticking out of it instead of a ball and the wire must move up and down to release the water. I've been trying to train my rats to use it for a couple days now, very patiently, but they can't figure it out and i can't figure out how to show them. I think they have to bite it or something because their little tongues don't seem to be strong enough to move the little metal wire when they lick it, i tried putting sticky treats on it to try and get them to work it but it didn't work. They understand that water comes out but all i can do is move the wire around and fill the valve with water and they come lick it dry. If anyone has successfully trained their rats how to use it I'd appreciate knowing how they did it. Thank you.