To do this i cut the black corrugated pipe added a t and aimed the pipe upwards to the downspout.
Gutter drain pipe depth.
The fastest way is to rent a trenching machine from a local tool rental.
Drain pipe slope maintaining a depth of 12 to 18 inches is best for drain pipes but the depth of the pipe may vary in order to maintain a downward slope which is critical for proper drain functioning.
If you live in a cold climate trapped water may freeze and burst the pipe.
In many instances i would dig a trench only 16 inches deep.
Continue until you have completed the trench.
I usually dig a trench about 12 to 14 inches deep for downspout drain lines.
It is most effective to place a drainage pipe in the ditch at a depth of 12 to 18 inches and then fill the ditch with gravel.
If you have hard clay soil or rocky soil you can use an electric hand held demolition hammer tool to dig a trench.
For the garage i used a downspout adapter without a leaf guard since there aren t trees close enough for that gutter to get clogged up.
This trench would follow the natural contour of the ground.
Since my in ground pipe ran right past the garage i had the garage downspout dump in as well.
The trench should be at least 6 inches wide and slope down slightly 1 to 2 inches per length of pipe so water drains away from the downspouts.
The solid particles may eventually clog the pipe.