I came across two additional problems with the backflow valve and weeping pump flooding prevention scheme subsidized by the city/region since the original article.
First the out flow pipe from your weeping tile pump is likely to create a lake of ice come winter. Not a problem on large rural properties, but a big problem on smaller lots.
I also noticed the instructions for the mainline backflow valve call for a drop from the input pipe to the output pipe. If an installer is cutting into a previously straight section of pipe in order to install this device how are they creating this drop? I've added in green lines to show the original straight section of pipe they cut into.
You might be lucky and have enough drop at the install location. But the installer might just be jamming in the preventer at an improper angle instead of tearing your entire basement up. You might think that small angles might not matter. However checkout the installation specification below. It's quite clear any “back angle” impairs the cleaning mechanism which is critical for correct operation.
Sorry to bring this news to you. As you probably know I'm in favour of preventing sewage via upgrades to the Region/Cities infrastructure. If you have or are installing these devices I'd make sure that the contractor is aware of how sensitive the levelling is.
Original Article: Flooding and Backflow Preventers