I did this repair because of the fuel smell. This thread was very helpful and accurate though the swap took me a bit longer. Things I would add for the next person, find a way (as above) to release the fuel pressure! Pressure remains in the fuel line that goes forward. I had the thing installed, but hadn't gotten that fuel line in fully, so the car would not start. I started to go through the work I'd done, first thing was that fuel line - was it fully in? No! It clicks when you have it in right, and mine hadn't. I gave it a tug, not knowing about the click and got to take a shower for my trouble as the yet un-clicked but now presurized fuel line pulled free! Ive been doing the tug test on things I've attached for decades but never, not once, found one I thought was inserted but it was not, haha!
Next, I'd definitely buy a tool to remove the hold-down rings. They are the metal variety. I skimped on a tool I thought I'd only use once, but it was cheap Ch. crap! I spent 60 minutes filing hooks into the thing and now it works great. $50 - $70 will get you a better tool. If you damage the rings new ones are available and not expensive, I saw when looking again at the tools I should have bought. The modified tool:
Use up at least 3/4 of your gas or more. Get a siphon tube with a bulb and empty the rest of the gas into a clean, correct container and cap it off! Remember liquid gas doesn't explode, it will burn, but GAS VAPOR EXPLODES!! And gas vapor is heavier than air...3 tablespoons of gasoline in vapor form == how-many-sticks-of-dynamite?! Work ina well ventilated are - outside would be best. Put at least 1.5 gallons back in your tank before you try to start the car, I read in Bentley that running the fuel pump dry will damage it.
I bought my 335i used. It had been used on a track in the desert and had dirt where I didn't know there were places, like caked up on the top of the gas tank, on the fuel pump and on the sending unit.
Work clean around fuel systems: scrape and vacuum all that dirt, use your roommate's toothbrush, moist & soapy paper towels, whatever, but get it clean before you crack it open so you don't get dirt and dust in the tank.
When I went to pull the three tubes back through with my string it slipped off. I thought I was truly hosed, but I put a twist tie around the three about 4" from their ends then tried slipping the bundle across a couple of times and voila. Wear some gloves and Keep Gas off of your skin. That was important when I was reaching into the tank. BTW, two of the tubes IIRC are clipped in place but don't fasten over an adapter. One is like a vent tube, the other...not sure