kitchen sink backs up with gray water when the washer in the basement drains. Washer drains into the sump pump

It happens when the sump pump kicks on. I replaced the check valve, but not sure if it's installed in the right direction. The arrows on the check valve are pointed down, towards the sump pump. Update: My bad, the check valve was installed correctly. Sorry. The washer does in fact drain into the sump pump. Would be happy to change that if I knew how.