Have fitted a 255L this morning so thought I would do a Wagon How-to as all the How-to's Ive seen are aimed at the Saloon. Apologies if this has already been done.

This is very easy to do with basic tools and no mechanical acumen. You will need a philips screwdriver, 8mm socket and ratchet/driver of choice, a pair of pliers, small jewellers screwdriver and somewhere to put the pump assembly once removed from the car that you dont mind smelling of petrol.

1. Ignore the Saloon instructions
2. Empty the boot of all the floor storage panels.
3. Fold down the drivers side rear seat back
4. Immediately behind the drivers side rear seat you will see a raised oval, roughly the size of a 6x9 speaker held on by 4 screws. Remove this plate
5. Unplug the electrical connection
6. Open the petrol cap to release the pressure
7. Try to start the car, if it fires allow it to run until it stalls
8. Use the pliers to undo the two spring clips securing the pipes connected to the top of the pump assembly. Slide off the pipes and dont lose the clips. The pipes can be tight and stiff, persevere.
9. Disconnect the 3rd pipe that is connected with a plastic clip/connector. Note - A small amount of fuel may be present in this pipe so you may want to protect the area with some paper towel. It is only a minimal amount however.
10. Undo the eight 8mm nuts holding the top of the tank on
11. There is a small plate held on by two of those nuts, move it as far as possible out of the way. It will not be completely out of the way, you will need to coax the top of the tank past it.
12. Remove the top of the tank, the pump assembly is attached to it. You will need to turn it as it comes out in order to fit the whole assembly through the aperture. Pause at this point to allow fuel to drain from the filter sock back in to the tank rather than all over your boot.
13. Check the thick rubber gasket that sits between the top of the tank and the tank itself. Ensure that it is firmly attached to the top of the tank using the three rubber locating lugs.
14. Take the pump assembly somewhere clean to work on it.
15. Remove the electrical connection on the top of the pump.
16. Remove the spring clips from the rubber hose on top of the pump and remove the pump from the assembly.
17. If you are fitting an aftermarket/uprated pump then there is a good chance that the filter sock supplied is noticeably smaller than the standard Subaru one. If this is the case use the small jewellers screwdriver to take the small circlip from the bottom of the old pump, then swap the Subaru filter sock on to the new pump. The new pump will have been supplied with a new circlip, use the pliers to push this on to the bottom of the new pump to secure the filter sock.
18. If your new pump was supplied with a replacement rubber hose, cut this to size, fit to the new pump then install the pump into the assembly remembering to reinstall the rubber boot. Note - the replacement pump I have used was supplied with a replacement rubber boot but it was not of the same quality as the Subaru one.
19. Reconnect the electrical connector and secure the rubber hose with the spring clip.
20. Refit the pump assembly to the car in a reverse of the instructions above.
21. Start the car, allow time for a smug smile.
22. Wash your hands to get rid of the smell of petrol then prepare a hot beverage of choice.
23. Put your feet up safe in the knowledge you've just saved yourself £50 labour at the local garage.

I have no patience and am useless at stuff like this but I still managed to have the whole lot done in under 40 minutes.
Some people recommend disconnecting the battery or wrapping the electrical connections with insulation tape. I personally didnt feel the need to do this as it is an ignition circuit so is not live without the keys in the ignition, however I take no responsibility if you electrocute yourself, blow yourself up or do any damage to your car