I am having an issue with my house in Brisbane. A plumber installed a new drain by cutting into an existing downpipe and fitting a pit. This was to help drain a small patio which would get a bit soaked during big rain events. However, it has made things significantly worse - when it starts raining heavily now the pit backs up and all the water floods back out of it.
The thing is, the block slopes down and the new drain is below the level of other stormwater lines that I think get quite charged during heavy rain, so I think this new drain has created a path of least resistance. In light rain everything seems to work fine. See sketch here - the 3rd downpipe from the left has been cut off with the drain added underneath, where it used to just be a sealed connection. I wonder if this also kills off the 'push' from the fall of the longest downpipe would have given to the column of water heading down the pipes so the flowrate has been affected?
I'm thinking I should remove this new drain and go back to a continuous connection. Even if the system does back up in a very heavy rain event, I'd prefer the driveway drain overflows than the patio drain.
Any thoughts before I pay the plumber to undo the work they already did (and perhaps should have known better about?)?
Cheers!