Gas Cap 1999 Toyota Camry

[rangermenace]

I need a gas cap for my sisters 99 Toyota Camry. It keeps loosing vacumm and causes problems with inspection also it doesn't make that clicking sound anymore. :toilet: I found a place that sells them but don't know vented or unvented? How do i tell

http://www.jcwhitney.com/stant-oe-r...5613.jcwx?skuId=2331445&filterid=d2168y1999j1