Downspout Into French Drain. We always make ours have a bigger slope. That tap can take 240 gallons of water per minute. A tv show suggested that instead of the pvc endcap the entrance to the french drain should be a catch basin with a grate and there should be an air gap between the downspout and the grate.
A lot of people have commented will the gutter system with a roof runoff system the underground will it overwhelm the french drain. I would begin a friendly conversation explain your concerns and ask the neighbor to look at a solution for dealing with their water.
Put the stone on top of both systems and then wrap it.
And then your french drain is isolated from your downspout system ensuring that your french drain is going to last forever. I had always worried that leaves and other debris would come thru the downspout into the french drain and clog it which would be especially troublesome during winter. That s just going to scream and when the water comes out of the pop up it ll just run through the stone into the french drain system. The most common way to get runoff away from your lawn and underneath your yard is by constructing a french drain.
