I now have a clean patio and a blocked drain.
The patio slopes away from the house. All along the edge of the patio and under about two inches of pebbles is a flexible hose.
As I understand it, this hose has perforations to allow water from the patio to run into the hose, and then it travels towards a drain. The end of the hose goes under a low wall and meets a much larger drain coming from further up the hill/garden.
I can access the joint of the two drains, by removing a patio slab. Water can flow freely down the "main" drain. However the water from the patio near that part of the drain is not sinking away. I think the flexible hose is blocked with decayed leaves from a plant in that vicinity. What can I use to try to unblock the flexible hose, without damaging it.
When a toilet blocked recently, I unblocked it by using warm, not hot water.
I have looked Youtube and found snake drains. I am trying to think how to improvise a snake drain for the short distance that I think the drain is blocked.
Sensible answers will be very much appreciated. Silly answers will mean that you cannot have a piece of the sponge cake I made earlier.