Pool and Spa
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The filter multiport valve has more than likely had a breach in the spoke gasket. This would allow water to run from one port (position) to another. So while you are in filter, the water is breaching the seal and running out your backwash line. This is a common occurance. Some valves have gaskets that can be replaced and others will require the "valve seat assembly" to be replaced. The model of the valve would have to be given for me to give you part numbers.
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