A portable liquid purifying device configured to purify a source of liquid in a remote location comprising: a filtration unit defined by a housing that contains a filter element for filtering a liquid, the filtration unit having an inlet for receiving unpurified liquid and an outlet for discharging purified liquid that has passed through the filter element, wherein a first header space is formed between a first end of housing and a first end of the filter element and a second header space is formed between a second end of the housing and a second end of the filter element, wherein an interior space is defined between the housing and an exterior of the filter element, the interior space being prevented from having fluid communication with an interior of the filter element in which the unpurified liquid flows, wherein the inlet is in fluid communication with the first header space and the outlet is in fluid communication with the interior space and not the second header space; a flush pump accessory that is coupled to the filtration unit and configured to operate according to a plurality of different operating modes, the flush pump accessory having a first conduit that is in fluid communication with the second header space; a bulb pump that is fluidly connected at a first end to the first conduit; a flush valve that is disposed along a second conduit that is fluidly connected to a second end of the bulb pump, wherein in a closed position, the flush valve prevents liquid to flow through the second conduit to a flush port; and a plurality of valve members including: a first valve (220,270) that is located between the bulb pump and the inlet so as to be upstream of the bulb pump, the first valve configured to restrict flow of the unpurified liquid from the bulb pump when in a closed position; and a second valve disposed between the bulb pump and the flush valve, wherein the first valve, second valve and flush valves are open when at least one of a flush operation and air purge operation is performed and at least the second valve and the flush valve are closed during a filtration operation in which unpurified liquid is filtered across the filtering element to the internal space and then flows through the outlet as purified liquid, wherein the first and second valves comprise one way check valves that only allow liquid to flow in a direction toward the flush valve. a filtration unit defined by a housing that contains a filter element for filtering a liquid, the filtration unit having an inlet for receiving unpurified liquid and an outlet for discharging purified liquid that has passed through the filter element, wherein a first header space is formed between a first end of housing and a first end of the filter element and a second header space is formed between a second end of the housing and a second end of the filter element, wherein an interior space is defined between the housing and an exterior of the filter element, the interior space being prevented from having fluid communication with an interior of the filter element in which the unpurified liquid flows, wherein the inlet is in fluid communication with the first header space and the outlet is in fluid communication with the interior space and not the second header space; a flush pump accessory that is coupled to the filtration unit and configured to operate according to a plurality of different operating modes, the flush pump accessory having a first conduit that is in fluid communication with the second header space; a bulb pump that is fluidly connected at a first end to the first conduit; a flush valve that is disposed along a second conduit that is fluidly connected to a second end of the bulb pump, wherein in a closed position, the flush valve prevents liquid to flow through the second conduit to a flush port; and a plurality of valve members including: a first valve (220,270) that is located between the bulb pump and the inlet so as to be upstream of the bulb pump, the first valve configured to restrict flow of the unpurified liquid from the bulb pump when in a closed position; and a second valve disposed between the bulb pump and the flush valve, wherein the first valve, second valve and flush valves are open when at least one of a flush operation and air purge operation is performed and at least the second valve and the flush valve are closed during a filtration operation in which unpurified liquid is filtered across the filtering element to the internal space and then flows through the outlet as purified liquid, wherein the first and second valves comprise one way check valves that only allow liquid to flow in a direction toward the flush valve.