The drain from my house to the main drain was blocked recently. A drainage company carried out a sonar trace to find the buried syphon, excavated the area around it and unblocked it using a high pressure water jet to clear a 6" foul line and restored flow. They are recommending that the syphon trap be excavated and removed in order to carry out a CCTV survey and then to install new pipework including bringing the rodding access to surface level. What does all this mean? Is what they are recommending a good idea? What does it all mean? Help!