GE model GLDA690MWW won't drain completely. water remains in reservoir at bottom of dishwasher. I have cleaned out main filter, cup and fine filter(per manual). We do NOT have air gap, nor garbage disposal. Should water (dirty) remain in that reservoir? I'm happy to go through the minor expense and trouble of installing air gap if that will resolve issue, but not sure if it will. Would appreciate any suggestions. Perhaps the water is supposed to remain in there, but it is cloudy/dirty and dishes are not getting that clean. Thank you. den