My frigidaire (Gibson) GDB755RJS2 dishwasher has begun not draining completely. Leaves about 1". Used a cup to empty and ran vinegar through the hotest cycle but the same amount as before remained on the bottom of the machine. Nothing in the glass catcher but thought I'd better contact someone who knows what they're doing before going further. Unit is 7 years old. Sink that discharge hose is attached to has been checked and is OK. Unit is 7 years old. Could use help but suspect new purchase is in my future.