The Mythteries of the Sewers
| Drains can block up but not sewers | The drain is small but the sewer is big? Don't you believe it.
The drain from your house to the sewer has a diameter of 100mm, the same as a margarine tub. The typical sewer pipe under the street in a residential area has a diameter of only 150mm, only a little bigger. When a sewer blocks then the sewage backs up and escapes from a sealed manhole, a gully trap, or a toilet inside a house. This requires urgent clearance and cleanup action, usually by the Local Authority and at its expense. |
| Sewers are big enough to walk in | Only in big cities like they have in Europe. To walk through a sewer it would need to be 1.5 metres in diameter, and
even then you'd have to hunch up. The one under the street near you has a diameter of only 150mm, a hundredth of that.
A margarine tub has a diameter of 100mm. Only rats can walk through that.
It isn't too difficult to imagine blocking it, is it? |
| To free up a blocked sink just pour boiling water down | Not so easy these days. When pipes were made of metal they would absorb the heat from the water, the heat would travel
down the pipe to the blocked bit, and the fat would fall away from the hot pipe. Pipes are plastic now. Plastic is an
insulator. The heat stays in the water and just takes a bit off the top.
Even if your house is old and has metal pipes, the result is just temporary. The fat sets solid again a bit further on and can block again soon. It doesn't go far away along your drain. The best thing to do is to avoid putting fat and oil down the sink. Put it in a Fat Trap instead and get rid of it in the landfill. That's the recommended thing to do. |
| Disposable items should be put down the toilet | Very wrong.
"Disposable" means that it can only be used once and then has to be thrown away. If you look at the label it always says you shouldn't put it down the toilet. In particular, don't put a loaded nappy down the toilet! The drain pipe from your house to the street sewer has a diameter of only 100mm, the same diameter as a margarine tub. The pipe going to the street sewer from your toilet is smaller only 80mm. How big is that nappy then? |
| Some things must go down the toilet for hygiene reasons | Wrong.
It is not unsafe to put sanitary items in a bin and later put them in the waste. If necessary, buy small plastic bags to put them in. Nappies can be sealed in nappy bags that you can buy from the supermarket. The sewers are not the place to put all this rubbish. They are designed like all sewers in the western world only for natural human waste, washing water, and the like. They are not designed for solid objects. Those all end up at the treatment plants intact. They have to be filtered out and trucked to the landfill. It isn't easy. Some of the small and thin items such as cotton bud sticks, panty liners and condoms escape. They end up on the beaches. No filter can stop them. Of course, if you don't put them in, they can't get out. |
| If it fits down the toilet it's okay for it to go down | Wrong. The toilet is not a kind of "wet waste bin".
The sewer is only for a few items, basically only the things that you can't reasonably get in the rubbish bag. It is for "natural" human waste and toilet paper, the water you wash yourself and your clothes in, water from cooking, and water from washing up pots and plates but without all that fat, oil and scrap food. |