I fought fires for years on a helicopter crew, and if dipshit trump knew what he was talking about, he would know that "flying air tankers" are fixed-wing planes, and having them release thousands of gallons of water even at a low air speed of 180 knots, it would blow the structure apart, as it is not built like steel-beamed skyscrapers.
Maybe the illiterate oaf meant heli-tankers, which can drop a few hundred gallons at a time at very low air speed or at hover (the thermals over it would be violent) but since a gallon of water weighs 7 pounds or so, dropping a ton of water at a time on a tall structure with high, thin walls and no interior structure to speak of would also pretty much ensure ending up with a pile of rubble.
He better stick to nursing his bone spurs.