I don't know what is causing your blockage, but I don't think there is a swing check valve in your plumbing drainage system. If there was one, it would be accessible. Another option is to hire someone who has a camera to inspect the drainage system. If the drain is clear, it could be a blocked vent.
Do you have the optional sewer backup coverage on your homeowners insurance policy? If so, you may want to ask them what it may cover.
Last edited by retiredguy123; 05-17-2022 at 02:17 AM.
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