Plumbing jobs completed last week. I found water marks right above the 1st floor room ceiling well as the ceilmg above the staircase. I asked the contractor to check. Today start wiring. From contractor's feedback, plumber said it's water tank leakage. Plumber said need to throw all the water in the tank, fill again to confirm. Contractor told me somehow the water tank cannot be changed. Is it true? Make sense? Pls advise, all the sifu here. I am so kan cheong already.