An improved canister-type aquarium filter design which includes, in various combinations, a motor which is contained within the canister, a discharge tube arranged approximately along the longitudinal axis of the canister, a pump section from which water exits from the top, a cover securing device which...http://www.google.com.au/patents/US5401401?utm_source=gb-gplus-sharePatent US5401401 - Hang on tank canister filter
