You also need to pull out the washer and lower the drain hose as far as possible. Then add some rv antifreeze until it runs out the drain hose. Takes about a quart. Dishwasher, same thing. There is always residual water in one. When you drain the house, you also need to drain the water heater, make sure it is off or it will burn out when power is restored. I turn off most systems except lights with the breakers anyway.glitches when power is restored are not uncommon. I would leave the well off too. You should have 48hours before freeze will occur in well insulated house at temperature you describe.
A portable air tank can do a passable job of blowing out lines. My old lake house we made specifically to drain, all the lines were sloped. Open the water heater, open a faucet, and open the drain valve at the water meter. fill the toilet and traps with RV antifreeze. Next spring, use some RidX to restart the septic.