I was told recently by Peugeot main dealer that it is 'impossible' to fit the locking ring and seal properly without tank removal.Also Peugeot do not have a special tool for this job.If you fit the pump with the tank in place you have no way of knowing if it has sealed properly until the customer brims the tank.With the tank out you can invert it to check for leaks.Fortunately the tank removes easily with the exhaust out of the way.