My experience is that dust/dirt is in the drain water and it eventually forms sludge/crud and especially in the off season. Never good to have any horizontal pipe in a gravity drain like that. Unless you want to clear it once a year with bleach it will eventually plug up.
Makes perfect sense. Do think it makes sense to open up the wall on the outside /other side where the minisplit is installed.
so that I can provide the drain in a vertical line !!
What is the best way to open the wall on the other side at the bottom or the top ?
If it is at the top, I need to run all the tube outside.
I don't know, cannot see it from here. Every one has a different wall and setup. Have to come up with a method and seal it so no water gets inside the wall. I don't do installs. I have a crew who does.
Post a pic of the wall and someone else here may be able to give you more info.
"Cut it twice and it is still too short".