Patent ID: 7661381

Claim:
A vehicle, comprising: a submersible housing, having ingress and egress ports; an impeller, which is disposed within the housing so as to draw water into the housing through the ingress port and to expel the water through the egress port; a filter, which is contained within the housing and configured to communicate with the ingress and egress ports so as to trap contaminants in the water as the water passes through the housing; a propulsion mechanism, which is coupled to drive the housing over an interior surface of a container in which the housing is submerged; a hollow tube, which is fixed to the housing and is configured to be filled with a fluid having a first specific gravity; and one or more objects, which have a second specific gravity that is less than the first specific gravity and which are contained within and capable of moving inside the hollow tube so as to maintain a constant attitude of the vehicle relative to the interior surface along which the vehicle travels.