Petrol tank leak

Could be a leak in the fuel line or even the tank its self. Climb under neath the car or put it up on a hoist and look for a wet spot in the area where it is dripping. Sometimes it could be up on the top area of the tank. It doesn't take a very big leak to make a mess and yes it gets costly. A few drops an hour can be several gallons a week.

Without know the specific engine I would say the carburetor float float valve seat is leaking. Usually a carburetor cleaning and rebuild usually fix this it leaking out the carburetor.

Now with some engines the gas tanks are two piece plastic that glue together that leaking over time and need replacing.

Either way you first must determine where the leak is.

I found a ..... leak. is that what you are saying.
comma , IS IT The pump leaking.
we dont know , we cant see , try photos?

there are many ways to get leaks,
id never guess. why one anyone on something so dangerous.
have you looked yet? or just see wet pavement.
OR LOOK ABOVE BOTH TOP OF REAR TIRES.
To see top of tank? and where it leaks.?
dont park in doors, or BOOM.
out side, far from buildings say 50foot.

think about smokers and gas fired water heaters in garages.
there are 2 fuel lines
and many vents and parts that can leak , filler pipe and hose.
evap parts. lots.

Yep,breather is necessary.Breather line is draining it under the car,less dangerous.Do not feel it to the top.Replace the draining line,dust/water may find a way into the tank,later u'll have to deal it (fuel filter,cloged fuel lines,fuel pump malfunction,fuel gauge malfunction).Track the problem eliminate the hipoteses of a cracked tank,loosed fuel pump.Cheers.

LOOK UNDER THE HOOD AROUND THE ENGINE FUEL LINES LEADING TO FUEL RAILS FOR PETROL LEAKS AND LOOK UNDER CAR AROUND FUEL TANK AREA.LOOK FOR LEAKS AT FUEL LINES.REASON VECHICLE NOT STARTING FUEL LEAK TAKING AWAY FUEL PRESSURE.FUEL LEAK HAVE TO BE AT THE FUEL PUMP FUEL LINES OR YOUR FUEL INJECTORS OR FUEL RAIL HAS A FUEL LEAKS AT THE O - RINGS.

HOOK PRESSURE TESTER ON THE COOLANT OVERFLOW OR SURGE TANK, FIRST REMOVE THE RADIATOR CAP.PRESSURE TESTER SCREWS ON TOP SURGE TANK.YOU NEED THE BLACK LIGHT TO SEE COOLANT LEAKS.

Well if you look under the car when filling or when its not leaking you will see that either were the leak is or where it has been leaking as you will see the stain marks were its been running and it will be either the pump gasket ( thats were the pump is fitted in the tank and the seal leaks when it get to that point OR the breather pipe on the top of the tank is broken or cracked,
BUT WOULD SAY ITS THE PUMP GASKET

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.

have you replaced the bleeder screws? and the expansion tank cap they both have O-rings that compress and will fail over time also check the hose at the top of the exp tank it also has o-rings inside it

your fuel sending unit could be bad or you have a leak in the gas tank.