Petrol tank leaking.. How do I best remove the tank to fix it?!

Hopefully your vehicle will have a drain plug in the bottom of the fuel tank*: remove this & drain the fuel.
With the plug still removed flush about 5-10 litres of fuel thru by putting in thru the tank filler hole as usual.
Replace the drain plug and put a FULL tank of fuel in (this will dilute any residue as much as possible)
*In the case of no drain plug the fuel tank will need to be removed & fuel drained out thru the filler neck, drain fuel, replace tank & procede from the 'put a FULL tank of fuel section of this instruction.
If the vehicle has been started with the bad fuel remove the fuel filter.
If the vehicle has an electric fuel pump* (more modern vehicles ie. Post 1985 [some vehicles still had & still do have mechanicle fuel pumps]) turn the ignition on with the fiter not in place, vthis will flush fuel thru the fuel lines pushing out the bad/old fuel. Take care as the fuel will be under a fair bit of pressure & "sqirt' out.
*If it is a mechanicle pump this can not be done in this way.
Replace the fuel filter with a new one.
Bleed the fuel system & start the vehicle.
Allow the vehicle to idle for 10-15mins before going back to your usual driving.
All shld now be ok but it is a good idea to routinely inspect the fuel system for leaks over the nxt 10 000km or six months (wich ever is earlyest) as in the case of puting petrol in diesel or diesel in petrol the different rubber and plastic items (such as 'o' rings) can begin to deteriate & leak in wich case they will require replacement.

All the best & I hope this is of some help & it works out for you...


Referances: Me, I am an auto mecanic.

There are sealants available from an auto accesory shop but the old emergency method was to rub soap into the leak. The soap reacts with the petrol and sets hard, I have seen it last for quite some time. The best way is to replace the tank with a good used unit. It can be soldered but the tank has to be cleaned out really well as the fumes can explode causing extreme injuries if not carefull. (not reccomended)

You don't say how much diesel you put in or how much petrol was in tank in the first place. If the amount of diesel is less than 5 % of the total then you may try filling tank with petrol and keep topping up to dilute the diesel. The best fix would be to drain fuel tank completly and refill with petrol. If tank has a drainplug , this will be easy but if no drain plug you will have to remove tank from vehicle to empty it.

turn key on and let fuel system presure build up thats the best time to check for leaks also maybe consider if problem not found quickly have checked out at a shop as fuel leaks turn in to bigger problems i.e.(car fires)

That sounds like the petrol pickup pipe in the tank has an air leak and when the fuel is dropping down below the leak it is sucking in more air than petrol.
The most likely cause of that is either the gauge sender untit or the fuel pump itself leaking (if the fuel pump on that car is inside the tank).

This sounds overfilled to me. Liquid should not get to the canister, only vapors, look for exactly what separates and stops liquid fuel, somewhere along the vent line... Sometimes on top of fuel tank.

BUT, it sounds like you are seriously overfilling. Gas comes out of the ground cool, then heats up in your tank. Put much less fuel in gas tank.

Fuel no longer lubricates anything, so no issue with full time LPG, but starting is commonly an issue, and most designs start with gas and cross over automatically to LPG, after warmed up.

Doc

It is not to difficult, you have to remove the two straps that hold the tank on and there are two nuts that you have to loosen with a deep well socket ad then you have to remove the fuel tank filler which requires a screw driver or not driver and removing the filler tube and overflow tube then drop the tank down mark and disconnect the wires and fuel line and that’s it. How every I would like to know why your changing it, then don't normally go bad and can be fixed with epoxy if it has a leak that you can get to.

Locate your petrol tank, then at top of it there is a hole where you can get access to the float level switch, before you removed it you check the socket on it, maybe lose connection.

A lot of Nissan models have an inspection cover in the trunk that you can remove to get at the fuel pump in the gas tank. If not there, perhaps under rear seat, but should be in trunk. Locate it, remove it and have a look for possibility of broken or cracked piece of fuel line hose attached to pump, or look around for other source of your leak. Careful with trouble light near fumes!! Use a good flashlight if you can. Be sure to relieve system pressure before doing anything on fuel lines if that's the problem.

The fuel filter is in the petrol tank. You will have to drop the tank to remove the old filter. Make sure the tank is empty as it is plastic so you need to have it as light as possible.