Have got petrol in diesel citroen Picasso what do you need to do?

I have a 52 plate Picasso and my slightly dimmer half put 20 pounds of petrol in my diesel car. There was about 5 - 10 pounds of diesel already in the tank. I simply syphoned the tank with a hose and a bucket. doesnt taste nice i know, then filled it with diesel and a fuel treatment and ive had no problems since. this was a year ago now. Its not usually bad this way round as truck drivers put a small amount of petrol in their tanks to stop them freezing in the winter. its when you put diesel in a petrol engine that you've got a problem.