An actual "dunk tank" large enough to immerse a human will be extremely heavy, possibly heavy enough to damage or collapse a house. (I just googled it, and got figures of 400-500 gallons for rental dunk tanks- that's 3,300 to 4,200 pounds of water, plus the tank structure, plus the person. And some substances might be even heavier than water.)
You would have to put it directly on a concrete slab on the first floor or basement, or otherwise you would have to consult a building engineer to figure out if your house's structure can handle the weight.
I think the OP means a gunge tank rather than a dunk tank.
Gunge tank: You sit on a bench with a tank or bucket of gunge above you, the mechanism opens and the gunge falls on you. Total amount of gunge used is probably no more than a few buckets full. Not that heavy and feasible on any floor of most residential buildings.
Dunk tank: You sit on a plank and then get dropped into a large and deep tank of gunge, enough to swim about in and at least 4' deep. Much larger and heavier, probably only feasible on solid ground.
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