The GM 1995 Aurora repair manual, says to use the access hole under the carpet in the back right corner of the trunk. You are best to buy a new fuel sender locking nut or ring at the dealer for about $8. The fuel tank does not have any drainage slots formed into it, so the locking ring rusted beyond any hope of re-using it. To remove the old ring, you have to pry it apart with channel locks, because it was so rusted that it would not rotate.
To relieve the fuel pressure, just use the press the center of valve on the fuel rail (for pressure testing) and a rag to catch the dribble.
Remove the gas cap and unhook the negative battery cable. Open the hood, snap off the plastic engine cover (if equipped) and locate the fuel pressure valve on the fuel rail.
Connect the fuel pressure gauge to the valve and set the bleed valve inside a sealable container. Relieve the fuel pressure and let the excess fuel drain into the container.
Make sure your fuel tank is no more than 1/8 of a tankful. If it's not, you will need to siphon some of the fuel out. Use the siphon pump to drain excess fuel into the same container.
Open the trunk and remove the trunk liner and the spare tire and jack. Locate the fuel tank access cover close to the back of the rear seat. Use the screwdriver to remove the screws from the access cover.
Unhook the fuel lines and label them for their position on the assembly. Labeling them will ensure you don't get them cross-connected when you are reinstalling them.
Unhook the electrical module at the top of the assembly. Have your container nearby for when you remove the assembly; the catch pan will be full of fuel.
Use the channel locks to remove the locking ring around the assembly, but be careful. Hold down the assembly as you are removing the locking ring. The assembly is spring-loaded and will abruptly pop up. Hold onto it until the locking ring is removed and let it rise up slowly. Remove the o-ring when you have the assembly out.
Clean the mounting area thoroughly with a shop rag. Install the new o-ring and set the new fuel assembly in position by twisting it and pushing down. Carefully replace the locking ring.
Reattach the fuel lines as labeled or marked, and then connect the electrical connection. Replace the fuel tank access cover, spare tire and trunk liner.
Replace the gas cap and reconnect the negative battery cable. Turn your ignition key on without cranking the vehicle. Keep it on for 3 to 5 seconds, and then turn it off. Repeat this process 2 or 3 times to repressurize your fuel system. The fuel system must be pressurized before starting the engine or it will have trouble cranking.
