The cleansing
I don't like to do this, but I'm afraid that the aphids might kill the plant - and could also invade the plants within our flat. After searching a bit about the problem, I find the information that one shouldn't use soap and water as it tends to kill important insects as well, and chemical insect killers are out of question. The best variant seems to be to wash the aphids off, and to spray strong black tea onto the plants. I immediately wash them off, and the next day I get a spray bottle. This helps for a while, but after a few days the aphids return. What do do now?
1: Get rid of them
2: Leave them be