You're fine. If yours is one that can be drained that way, it works great. If yours has a check valve, it's on the hot outlet, not the cold inlet as someone said. Just remove the low point drains and flip open the relief valve to relieve the vacuum. You can also open a tap to do the same thing. The tank will drain down to the level of the cold inlet which is same level as the anode plug.
If you're not sure how well this works, do it once and then pull the anode and check.
Yes, you should still check the anode once a year or so. If you're one who likes to leave the tank empty between trips, it's an east, non-messy way to do this.