A water leak was found on a fitting connecting ITW dump return line pressure gauge on top of exit module. TM tank flange, o-ring slot and o-ring were contaminated by water and water rust. Frank and I cleaned the flange and o-ring slot . We changed a new TM tank o-ring, vacuumed around other 3 module flanges. The leak fittings with pressure gauges were removed . I put a blind cap on removed fitting spot.. Water are switched back to ITW. No leak on blind cap.