my dishwasher will not drain completely and the manual only says that it could be a problem with the air gap. mine is a residential washer and as far as I know I do not have an air gap but I am not sure what that is and the manual doesn't tell me. I have cleaned the filter screen but it doesn't seem to come out to check under it for a clog. When I disconnect the drain hose under the washer the water only drips out wit the washer off. Should it flow out better? What could the problem be?