Sewer time again

Yesterday, we had to have Watercare come out to clear blocked sewer lines, something we found out about at 7am when Nigel was about to leave for the day and saw a growing puddle. I went outside when there was enough daylight and found sewerage bubbling up out of our gully trap and running across our lawn. This was similar to what happened last September, although less severe.

Watercare says these blocks happen because people flush things that should never by flushed, like sanitary pads, tampons, wet wipes, nappies, etc. (see their poster at left). Such things block the pipes—which aren’t very wide—causing sewerage to flow overland—in this case, our yard.

Another problem is that the access points—“manholes”—have often been buried, sometime by the builder/developer, which means property owners may have one on their property and not even know it. Watercare can come and dig up a manhole, and the owner can’t object (I don’t know if the property owner is charged for that or not, and I didn’t think to ask). The Watercare people told me that at one house nearby the owners had a shed on top of the access, which is illegal (they can order it be removed).

We know from our September experience that we don’t have any sewer access points on our section.

I shared most of this information on a local community page, and my personal Facebook, mainly as a way to ask that people don’t flush anything except for what Watercare delicately calls “human waste” and toilet paper—nothing else. As I said on the community page, “We’d rather not see your, um, stuff, flowing up out of our gully trap!”

What I didn’t say in the post, because most people here know this already, is why we even have a gully trap.

Basically, a gully trap works like a sink: Sinks, showers, and/or laundry (also known as “graywater”) empty into it, and as it fills with water, gravity pushes the water into the sanitary sewer. It uses the same principle as the S trap under a sink, or the water in a toilet bowl: The water blocks sewer gasses.

The reason for them is because of exactly what happened to us: If there’s a sewer blockage, the sewerage will back up through the gully trap, rather than into the house. This is why it’s placed between the house and the connection to the sewer line. By code, at least one graywater pipe must drain into the gully trap to keep the water level up because if the water evaporates, it’ll smell.

In cold areas where water freezes in winter, gully traps won’t work. In North America, for example, they use a backflow preventer, which is kind a specialty flap that closes if the sewer starts to back up into the house. The problem with that is that the pressure caused by the blockage can cause manholes to be lifted—even violently, and with a sewerage fountain. Nice!

While I learned some of that over the years, I didn’t know most of that until the overflow last year. I wanted to understand what was going on, so I read up on it.

So, the sewerage overflowing the gully trap is a good thing—it protects the house—but it only happens when there’s a blockage, which is a bad thing. Most blockages in residential lines are caused by people flushing things down that toilet that don’t belong there. As one of their more colourfully worded posters (PDF) put it, “Only toilet paper, pee and poo should be flushed down the loo!” And so it goes.

See also “Toilet humour” my post from June of last year about this topic and newspaper ads about it.