We have found if the underground pipes are completely clogged they are beyond cleaning and should be replaced.
Blocked gutter drain pipe.
Expose the bottom downspout opening divert the flow away from any landscape drain and then use a garden trowel to reach up into the opening and remove any clogged leaves and debris that could have accumulated there.
Then you can try to clear the clog with a plumbing snake or by using a hose to send water into the pipe and dislodge the clog.
To unclog a gutter downspout try your easiest options first.
If your downpipe isn t draining or water is flowing out the back then it s probably clogged.
You can try removing the downspout from the drain pipe first.
Remove the guard at the other end of the drain pipe if there is one.
Start by cleaning the bottom downspout opening.
Disconnect the gutter downspout from where it connects to the drain pipe.
Also they re not always caused by debris in your gutter system you could end up with a clog due to a tree root growing into the pipe.
Turn on a garden hose to its most powerful setting and run water through the drain pipe.
Check to see if water and debris come out the other end of the pipe.
Over time leaves dirt and other debris can clog up the pipe.