| Before you attempt to unblock main drains, | | | | Interceptors were once used to cut houses off |
| make absolutely certain what system you have | | | | from the main drains; this is no longer done, |
| and get to know how it works. | | | | so they are no longer fitted. But you may |
| | | | find that you share an interceptor with one |
| Two pipe systems are still very common on | | | | or more neighbouring properties. Interceptors |
| house built before the second world war. | | | | are easily distinguished from ordinary |
| There are two separate waste stacks running | | | | inspection chambers by an air inlet terminal |
| down the outside of the house – one | | | | nearby. |
| for waste water and one for soil. | | | | |
| | | | The single stack system is the one now in |
| The waste pipes from your plumbing fittings | | | | common use. As its name implies, waste water |
| run into the waste stack either directly or | | | | and soil pipes all connect to the same stack. |
| via a hopper head (now obsolete but still | | | | Until recently the stack had to be inside the |
| very common). Pipes from ground floor | | | | house but the rules have since been relaxed |
| fittings often connect to the stack under | | | | to allow outside stacks. Ground floor |
| ground. But if they are far away from the | | | | appliances too far away from the stack to |
| stack they run instead into a separate gulley | | | | connect to it have their own sub stack or run |
| – a kind of underground U trap. | | | | to a closed (back inlet) gulley. All |
| This joins the underground pipe from the | | | | underground pipes run in a straight line to a |
| waste stack at an inspection chamber, covered | | | | meet at an inspection chamber. |
| by a manhole. | | | | |
| | | | There are as many variations in drainage as |
| Soil from the WC always runs to the soil | | | | there is in plumbing. Houses with a two pipe |
| stack direct. The underground pipe from the | | | | system which have been modernized may also |
| stack joins the waste water pipe at the | | | | have an internal single stack or sub stack. |
| inspection chamber. Rainwater may be | | | | Some larger houses have the one pipe system |
| collected at a gulley to join the waste water | | | | in which a single stack runs on the outside |
| system. It may run from the gulley to the | | | | of the building. Some early single stack |
| inspection chamber via a separate pipe. It | | | | systems have additional old style gullies. |
| may be dispatched to a separate gravel filled | | | | |
| pit or soak away. Or, in areas where water is | | | | There may also be more than one inspection |
| in short supply, it may run to a separate | | | | chamber: they must be installed where ever |
| storm water drain. | | | | pipes join and where the gradient or |
| | | | direction of the drain changes. |
| From the inspection chamber, the combined | | | | |
| waste and soil water flows towards the main | | | | The only way to really be one hundred percent |
| drain, normally in the road. Before it gets | | | | sure on how your drains are laid out is to |
| there it may well pass through another | | | | piece them together on a sketch plan, using |
| chamber – the interceptor | | | | the above information as a guide. |
| – containing a large U trap. | | | | |