Blocked Drains Interceptor Siphon?
Interceptor/Siphon traps were originally installed to prevent sewer smells from entering into poroperties. In those days it was not sure of the health risks associated with foul air. There was also opposition to drain interceptors because they cause waste matter to sit in the outlet of a chamber until the next flush.
It was therefore, left to individual authorities as to whether they allowed the installation of traps or not.They come in many shapes and sizes
The interceptor traps created their own problems partly because they were often installed on combined storm and foul drainage systems and as a result silt and debris would collect in the trap causing blocked drains
The trap shown to the right is a basic interceptor found on the outlet of a chamber with a rodding point fitted over the top to access the outgoing pipe work, in the collar end of this rodding shaft would be a clay ware cap or tea pot lid as they are known which would form a seal until access was required. However these lids would for one reason or another end up in the trap itself or they would just go missing all together creating a direct vent and defeating the purpose of the interceptor.
You often find these traps to be blocked solid with the waste water flowing through the rodding point and into the outlet pipe, this can go on for years causing silt and debris to build up in the system upstream of the chamber. This is of course fine if it stops the system overflowing, however i have works on numerous property subsidence jobs where the movement to the building could be attributed to the water loss from the partially blocked system.
Any kind of interceptor/siphon can create blocked drains when the system blocks downstream of the trap. A trap with no rodding point is useless when it is at the bottom of a blocked 2 meter deep chamber. However, it is possible to feed a high pressure jetting hose around the trap especially if it is a 150mm or larger diameter pipe however this is quite restrictive with regard to a effectiveness of the jetting unit. It is therefore necessary on occasions to have the chamber pumped out prior to breaking out the trap in order to clear a blockage.