Should one pour Gumout into the gas tank?
Gumout Fuel System Cleaner, Yes.
Gumout Carb Cleaner (Spray), NO.
Please read and follow the label directions.
Gosh, just follow the directions on the can.
Not if you don’t have a good reason to do so. Adding chemistry to the fuel does not help a properly functioning engine.
If you want a really good useful answer, I would suggest telling us why you are asking the question and exactly what specific Gumout product you are referring to, since they may many different products.
I would suggest that the addition of a fuel system cleaner is an OK thing to do as a part of normal maintenance but will not substitute changing fuel filters or normal tuneup time. I use seafoam once a year in the fuel system of my toys and change the filters as recommended by the manufacturer, and have never had a fuel problem. Rocketman