The act of emitting intestinal methane gas, i.e., a fart, while underwater, especially in the bathtub, causing the gas to bubble up through the water only to emerge with increased sound and odor as it hits the air. Playing the water trumpet takes on added enjoyment when one positions one's anus so that the emitted gas tickles up one's backside as it rises up through the water.
Phil enjoys playing his water trumpet while taking a bath with his wife, Sheila, causing her to bolt up and out of the tub, screaming, "PHIL! Stop farting in the bathtub!! It stinks!"
by sorkab September 03, 2010
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