Flip your water heater to bypass and drain it from the outside plug-anode rod. Then blow your lines out (with the water heater in by-pass). I think you are making it harder than it has to be using the low point drains. Just put the blow out plug in your city water connection and turn on the various faucets.
The water out-take is at the top of the tank, the in-take is at the bottom. all your doing is pushing air through the water. You need to drain the water heater by the plug and then by-pass it.
FYI, I "pink" then blow out the pink. When done, I just open the low-point drains and let the remaining pink out. "Pink" goes down the drain p-traps that way.
