Hi folks, I live in a house with 3 toilets, One main, one in the en-suite/Shower room upstairs and a WC downstairs. Today I noticed that when I flush the WC in the main toilet upstairs air and a small amount of water comes up through the Bath plug hole. I guess you would call it a standard layout for a main bathroom, all pipe work is hidden behind the wall. Now.., the main toilet is never used, as I live here alone I always use the others. But I can say with certainty that it was not like it 6 weeks ago when I was doing some painting in the main bathroom, I have lived here for 10 years and not had this problem before. When the WC is flushed, the water raises to a level just under the rim, Air and some water comes out of the bath tub plug hole..... before the water in the WC returns to what I would call its 'normal' level. First thougths were a blockage? but as I say the main bathroom is 'Never' used. There are no foul smells and neither of the other toilets have the same problem, I hope the pics help to explain the problem. Would appreciate your thoughts Thanks in advance.