I dunno, maybe 80 gallons. I just duplicated this problem today while cleaning a sofa. Unit shut down just as I finished the sofa. Tank was full, but for the first time in 6 yrs, water was coming out the blower exhaust. Foam, from to much upholstery shampoo, and I forgot to turn the pump out on. Yes, it does fill the tank after just one sofa, due to the bypass. I do run with the diverter on. So excess foam does look like water pouring out. In to the dish washer the heat exchangers go.......