From what I gather the tubes on the arizer are 9/16th in diameter.
Think these caps would work for it: http://www.grainger.com/product/Vacuum-Cap-5RKR3
(half inch) - http://www.homedepot.com/p/Everbilt-Off-White-Rubber-1-1-2-in-Leg-Tips-2-Pack-49225/203661036?N=1z0xd5qZ1z114to...