We have tried to force air into tank after after water failed and neither will go througdip tube.

We have tried to force air into tank after after water failed and neither will go througdip tube. If you can't get water past the cold water inlet why would you expect to get air through? Please explain how you tried. Did you remove the fitting from the cold water inlet and check the dip tube,
NOTE- If you soldered the 3/4" threaded adapter directly on the inlet there's a good chance you melted the flange on the plastic dip tube. Remove the fitting from the cold water inlet and check. Let me know what you find. Good luck, Tom