Let me chime in here about what I have learned.
All heat pump WHs will need a drain for condensate. This is because they work using the mechanics of refrigeration to move heat from one area to another. The evaporator coil in a refigeration system gets very cold, when you move air accross a cold suface, moisture is condensated out of the air. This holds true for all refrigeration units (Freezers, Refrigerators, HVAC Heat Pumps, Air Conditioners, and Heat Pump WHs.)
So just like your car will have water dripping out of it on a hot day after running the AC, the HP WH will also produce condensation. From what I understand, it doesnt produce that much, but I think that how much condensate is produced is dependant on the humidity of the local area. More in humid coastal areas, less in arid desert areas.
I just purchased one of these units and have the same issue that you mentioned. I plan on piping it to the drain line that my HVAC Heat Pump uses. It is just a 1/2 inch PVC pipe that runs under the house and dumps on the ground in the back of the building. I also plan to utilize my existing tank as a storage tank.