Drop drains

[1974stephen]

My mother-in-law has a drop drain at the front of her house, and it occasionally gets blocked. There are two outlets, one at the bottom of the inspection chamber, that lies at the same level as the main drain, and another outlet approx half way up the chamber.

At the moment, when you flush the toilet water mainly comes out of the bottom outlet, but a small amount comes out of the top one, that then falls into the main drain below.

My questions is, does this indicate that there is a partial blockage in part of the drain, as my understanding was that the upper outlet was as an overflow if the dropped part was blocked.

Any offerings on my understanding?

 

[noseall]

Sounds like a typical interceptor trap, as design that died out after the last war.

We have hoiked up a few of these and re-hashed the drains to modern standards as they are nowt but trouble.

 

[1974stephen]

House was built in the early 80's I believe. Would that still sound right?

 

[maltaron]

I think that is what is known as a back drop. I allows a high level drain to flow into a lower level chamber at invert level. The upper pipe is a rodding eye and should have a removable bung in it. If the bung is missing them some flow will occur from it. Nothing really to worry about.

 

[1974stephen]

That's exactly what it is, the term 'back drop' is what the last guy who came out to jet it called it. It's all come flooding back now. If it's usual for some water to come out if there's no bung in, then that's fine.

Since the water saving cistern has been installed, it blocks more often than it should; despite my best efforts to get it to fill brim full!