Now I have heard you are supposed to wait until you have about a 1/4 of a tank left before you change the pump/sender. I didn't. I should have Its messy and a bit hard to see what your doing because the pump was submerged in petrol so if were to do it again I would have the tank as empty as possible. You might what to disconnect the battery although I didn't.
First you have to remove the rear seat bottom, a fair amount of force needed on the Touring as it has some clips on the front, I think the Saloon is easier. You need to push the front bottom of the seat towards the back of the car and then lift up:
Then you have to remove the sound deadening from over the tank hatch, if its not been out before you will have to tear along the perforated line and cut it to remove it from around the wire:
Then remove the 3 screws that hold the plate and you can lift it to see the fuel tank. Unplug the wire by sliding the tab back and pulling up. Pry the BMW clip off the hose and pull it off the sender, a bit of fuel will spill as its under pressure:
Now use a hammer and screwdriver/punch to undo the metal locking ring:
The inner plastic ring is the sender unit and the outer ring is part of the fuel tank so don't try and lever the whole thing up! :
Gently pry the sender from the tank and pull it out being careful as its a odd shape and will catch. Once you have it out you have to reach in and press two plastic tabs on the pump to release it from the tank, then lift it all out:
Here are the tabs circled:
Here you have the complete pump and sender assembly out:
This is where the pump clips in, also note the plastic ring on the top of the tank that the sender sits in(the part I told you not to lever at earlier!):
Fit your new pump back in the same way it came out then slide the hose into the tank and feed in your sender. It is very tricky to get the sender back in so just be careful you don't damage it. You cannot see where the plastic end of the sender is going so you just need to feel it and align the notch on the sender with that in the top of the tank(see above picture towards the back of the car). Another hard bit is getting the seals fitted correctly, it is in two parts, one on the tank and one on the sender, however the sender seal needs to be fitted into the tank seal and then the sender pushed into it very carefully! If you feel the sender suddenly "pop" in, you've more than likely pushed the seal out and will have to reseat it. If you don't the tank will leak when the engine is revved and petrol will fall out onto the floor(ask me how I know )!!!!
Here is a picture of the sender seal, it fits into its opposite shape on the tank seal:
After that tighten your locking ring and replace the pipe, connector and covers/seat. You will be able to hear the pump start when you turn the key to the run position.
I don't know how you can check that the seal has seated correctly apart from leaving the covers off and starting/running/revving the engine or taking it for a short drive and then checking for leaks.
Also there is no way of knowing if you have the sender in the correct position as the end is spring loaded and will probably fit in incorrectly. This will push the float arm up and give you a lower fuel reading than is correct. As I said I don't know how this can be checked apart from maybe filling the tank right up and checking the levels are the same for each sender using the hidden OBC feature?