Gutter cleaning is not something we look forward to as a job but it is a very critical part of gutter maintenance.
The biggest problem with seamless aluminum gutters is that they tend to fill up with leaves, sticks, roof particles, and other debris.
Keep in mind that most of this debris could be kept out of the gutter system by simply installing gutter leaf screens.
Even with leaf screens installed, you should still take a look inside your gutters at least twice a year. (Typically in the Spring and Fall).
If you do find debris in them, just take a water hose and spray right through the screen and wash the debris right down the downspouts. Be sure to disconnect any downspouts that are connected to the underground drain line first.
Occasionally, debris such as pine needles may need to be manually cleaned off.