Devices for cleaning vessels, especially swimming pools, are discussed. The devices may include repositionable in-line valves, with the valves typically moving laterally (from side to side) and changing the initial direction of the main fluid-flow path through the valves and corresponding cleaner bodies. Asymmetric feet may be utilized as part of the devices, whose bottom bearing surfaces may include elongated strips of material placed parallel to the normally-forward direction of travel of the devices. Discs of non-uniform flexibility also may be employed, and blocking tabs or gripping material may be used to inhibit undesired backward movement of a cleaner when its operation commences.