What he's referring to as the "dip tube" I think is the cold water pipe. You need to take water from the bottom of the tank, since gas will accumulate at the top. If you remove the pipe that goes to the bottom, you'll get nothing but gas out.
This is basically an oversized version of the old-fashioned water-filled hand-held fire extinguishers Class A.
Have you considered other substances besides water? An 80 cubic foot room measures 10 feet on a side and 8 feet high; an inch of water on the floor is about 63.5 gallons.
How effectively can you make sure that water will get to or stay at places other than the floor? Would detergent or some other such substance help?
This whole thing relies on a single fire sprinkler head of an industry standard design that is capable of delivering 25 GPM and will cover the entire enclosed area, floor-to-ceiling thereby smothering the fire.
If the fire has a secondary source of fuel and air, all is lost.