This works involved taking down the whole PVC gutter as part of the car porch sank by several millimeter. This has pulled down the roofing at one side but hardly be seen until we checked under the driveway. There is a cracked to show that one side of the driveway and car porch sank.
This slight earth movement has caused the gutter to lower than the water outlet direction. It has become the catchment area for the water and during the dry season, it still filled with water from the air condition water outlet.
This was discovered when there are a lots of bird flying over and landed on the gutter and at the same times pooped on the gate.