I have not seen this mentioned tho I may have missed it. If it has been, here it is again.
RE backfeeding house from a swimming pool , dryer, etc. or worse from a 120 v plug somewhere handy. Even if you throw the main or cut loose from the street power to avoid killing power linemen you still have created a probable extreme fire hazard to your home. The plug you are backfeeding is fed by small gauge wire. In some cases as small as 12 ga. or even 14 ga. The power source should start at the point of the heaviest ga. wire & work it's way down to the appropriate ga. for the appiance operating at that location. What you are doing in the case of starting the power load thru small gauge wire is creating extreme heat in your wiring. I mean extreme heat. This can burn down your home or your neighborhood. Sometime just plug a 1500 w. appliance like a hairdrier or space heater into a 14 ga. extension cord for a while then feel of the cord how hot it has gotten. The longer the cord, the hotter it will get. Too much resistance in small gauge wire. And that is just pulling 1500 w. A water heater has two 4500 w elements in it alone & clothes driers, heat & air units & ranges pull more than that. Spend a couple hundred on some sort of transfer switch. It's cheap insurance. I have a 15,000/22,500 Generac gas power on a transfer switch with a sliding plate that prevents me from have both generator & street power on line at the same time. Remember, ALWAYS feed thru the heaviest gauge wire 1st & your properly installed house wiring will serve just as it does from street power. No melting, stinking hot wiring in your walls & attic just waiting to ignite something.