Wrong, wrong, wrong. I have just been on this very expensive rollercoaster and I can tell you what I have learned. Similar situation, end house with sewer and surface water drain in my back garden serving mine and 8 other houses. Rang the council when it started to overfill and was told by some dope that I would have to get the plumber myself. Did so, cost me E306 and drain still wasn't fully freed. He felt the block was outside my wall on way to main drain and I should call SDCOCO.Plumbers not allowed touch council drains. Did so, and was told off by a very nice man who said I should have called SDCOCO first as they will free the drain, be it in my garden, neighbours garden or council property for the fee of E120 and will work for as long as it takes for this fee. The fee must be divided between the 8 households and they can be prosecuted by Environmental Health if they don't contribute. They came out and found they also had difficulty getting a good flow, they didn't charge me anything yet as they are going to come back soon (I hope) and have another go. The man you need to phone is Sean Jones tel: 4570784/5/6. He told me sometimes people in the council do not give out correct info about this problem (Reassuring isn't it?)