I know this is a silly question, but I borrowed this vacume from my Mother-In- Law, and she told us to fill the tank up over the little bump. Do you actually cover up the bump or do you leave the top of it above water? I'm not sure what you call the little thing that protrudes up in the middle of the tank, but that is what I'm calling a bump! I'm sure if I had the manuel that came with the vacume I would know how much water it takes. I don't really want to question my Mother-In-Law's intelligence by asking so can someone help me out? There is a fill line on the tank and it looks to me like it's under the bump. My husband thinks that it is over the bump!

Vacuums - Rainbow - 75th Anniversary Canister Vacuum