I'd try the garden hose again. Concentrated spray head and jam it in repeatedly please.

1. I feel a Plastic Rotary Cutter would work without any damages to agitate the collection to move down the line.

2. How much distance will you need to travel? A 2nd or 3rd entry might be needed to do a better job cleaning.

3. It sounds as if Hardware Cloth or Etc might need to restrict what travels through the line.

Good Luck!

The line is about 70' from the down spout to the discharge point. I was not aware there were plastic heads. Is the head plastic, ,or is it designed for plastic pipe?

If it's leaves, a hose will generally get it.

But if a hose isn't getting it, you are probably looking at a critter that is clogging it up.

Or in our case gum balls. We have are having some one take a look at it next week and make a recommendation of action.