Heated tanks???

For what it's worth: My electrically heated tanks (the 120 volt side) automatically comes on whenever the RV is on 120 volt AC power AND the temperature is less than 40 degrees. Only the 12 volt heaters, used when traveling, have a control switch on them to prevent running down the batteries when dry camping. Not all systems work the same I suppose.

If you have the electric type heating pads on the bottom of your tanks, you dont want to turn the heating element on unless there is at least enough water/waste water in the tank to completely coat the bottom of each tank. With nothing in the tank to absorb the heat,the heat element will soften the plastic at the bottom of the tank to the point that the bottom will eventually sag in the center and will no longer drain properly.
I found this out from a friends rig that had odor problems no matter how long he flushed his black tank. When we inspected the tanks we found that his tank was sagging about 2 inches in the center therefore would never completely empty. The tank was so soft that you could push it in with your hand with very little resistance. We were scared it may burst any second.

Most tank heaters say not to turn on if tank is empty, but as said above you don't need to heat an empty tank.

Even if you have some liquid (say: less than 1/3 full) there is plenty of expansion room (called "head space") and heat is not really necessary.

Our heated tanks are the black/Grey. We don't have a heated fresh water. And we will have them turned on shortly.

If there is nothing in them, there is no reason to turn them on...