I agree with the above, drain the tanks and, then close the drain. You might also want to consider keepin your drain "flapper" open in the bottom of your toilet. I've placed a "crushed beer can" attached by a shoe string in it's throat to keep it open. I tie the shoe string to my towel rack just behind the toilet. The beer can's contents is consumed on the spot..lol
I always put a little (pink) RV antifreeze in each of the drain bowels as well..(kitchen, bathroom and, shower)
This may seem like an overkill but, I also remove the shower wand plus leave the controls open..
I drain the water from everything and, then attach compressed air (40 to 50 psi)to the city water intake and, continue this until step until it's blown dry~!! (even the hot water tank) This step is done first before adding any antifreeze.
just remember to close everything up in the spring..lol
Hope this helps..