That is your fuel evaporation canister. Normally you have a hose that goes from that to your air filter housing, which causes a vacuum on the canister, drawing out the evaporated fuel from the fuel tank. I think so anyway.
The missing hose (A paper acordian style hose) Goes to the side of the air cleaner housing. It allows the fuel tank fumes trapped in that cannister to go into the carb and get used.
That's what I did on mine too. No problems with this. Gave me some peace of mind knowing it was sealed up. I was worried that water could somehow run thru the line back into the tank. Paranoid maybe, but hey...that's me! Hahaha!
those are fuel vapors...water going back to tank would be the less of the two evils...fumes exploding under the hood would be...worse case...