hi can anyone advise in 2004 we had a 2 storey side and rear extension built, the kitchen is built over the sewers and the water board were fully aware and sent out the machine to put a camera down to check all was ok, 2 additional access points were put in place either side of the building, since then it seems that there is a lip in one part of the sewer under the extension and it keeps causing a blockage, we had to keep getting someone out to rod this, who is at fault and what options do you think i have to get this resolved. thanks