1999 Toyota Corolla water sound in my vents

Air Conditioning problem
1999 Toyota Corolla 4 cyl Automatic 134, 00 miles

Since the beginning of the year I can hear water in my vents. When you press on the gas after you've come to a stop you think you're about to get a shower. Ive taken it in about 4 or 5 times now. They say they dont hear the water but they check the drain pipe to see if its clogged and they get whatever debris out of it. Last time I brought it in my passenger side floor was soaked because a tube was missing. They said thats why I hear water but now it should be taken care of. I left there hearing the "gushing" water sound. Any idea what it might be?