To actually remove the tank - you've gotta disconnect the two fuel lines (golf-T's serve very nicely to plug the lines while it's apart - which I'd recommend, and no, gas won't leak out of the unplugged spigots on the tank - but I usually slip a few little pipe-caps over the ends. you want ones about 1/4" ID). and you've got to disconnect the power line to the tank.
All of these are in the forward left side of the tank. and they are easiest accessed by removing the left lower panel on the fairing. which requires:
OK - cautions - you do NOT want to get any dirt into the FI lines. the lines you're disconnecting are AFTER the fuel-filter in the tank, and dirt getting into them will instantly go to an injector. This is not a good thing.
There may be a bit of fuel spilled - the fuel-rail will be under pressure if you've run the bike in the past hour or so - if you leave it sitting overnight - the pressure should have bled back into the tank. Be prepared with a nice throw-away rag when you loosen the first hose clamp. Alternatively, you can start the bike and unplug the electrical plug. When the fuel pressure goes to zero, the engine will stall.
Inspect your fuel lines - you have a 13-14 year old bike. If they look the least bit doubtful - replace them with FACTORY fuel lines. these are special lines meant to take FI pressure (which in the case of a failed pressure regulator could exceed 60PSI.)
That's about it. it actually took longer to write it out then it should take you to remove the tank.
NOTE to others - the later ('86 and newer) tanks mount differently at the rear - two clips instead of the 10 mm bolt. Other than that the procedure is identical.
BTW - if you just had to slide the tankbag straps under the tank, you could loosen the rear bolt and slide it back a bit and lift up - the back of the tank can be lifted about 4" without disconnecting the fuel-line hoses.
BTW2 - you MAY find that there are two small lines connected to nipples on the right rear side of the tank - these are the overflow line and the tank-vent line. Usually - these are not connected, but are directed at a little funnel arrangement that clips to the frame below them. IF you find they are still connected - I'd suggest getting the funnel thingie. it was a retrofit for early models.
BTW3 - there should be aluminum and fiberglass insulation attached to the bottom of the tank. This was also a retrofit to early models. if you don't have it - it may still be an 'open campaign' and you might just get your dealer to install it for free via reimbursement from BMW.