“Kitchen sinking” refers to a situation where one or both partners bring up multiple past issues or grievances during an argument, often resulting in the original problem being overshadowed or lost amidst a barrage of other complaints or criticisms.
For instance, one partner might say “I’m upset that you forgot to get the groceries again. It’s frustrating because we talked about this last week,” and a kitchen sinking response to this might be— “I just had a busy day at work, I forgot. But you know what’s really frustrating? You never take out the trash when it’s full either. It’s always left for me to do.”