Screw the tank gauge onto the tank - C5 Break 2.2 HDI 2013

[Albireo]

Hi! (excuse my bad english)
Recently bought this car, so I have no history.

The diesel will leak when the tank is full.
Having problems with screwing the fuel gauge into the tank, on a Citroen C5, 2.2 HDI break 2013.

I have bought a new cover (nut) - 1531 30 - with a seal 1531 40

What is required for it to be mounted?
The nut feels too small, which means that it is not easy/possible to screw the tank gauge.
(and leaking diesel will be the result, when the tank is full)

The old holder looked like this .:

Also the gasket must be stretched to reach around the neck of the tank gauge connection. (even it is quite tricky to assemble).
The seal has a small seat side that should press against the neck. When it's where I think it should be, it looks like this

Could there have been any damage to the threads on the tank, where the tank gauge is to be screwed on? - (therefore the nut does not fit?)
Is a special tool needed to screw on the big nut on the tank gauge?
It feels like the gang takes, but after 1/4 - 1/2 turn the fingers have to be repositioned, and then it "pops" up - or I push too hard and it starts to go crooked..
Should it be easy to put on? or do you have to use some tool? (eg hammer and chisel?)



To better see whats wrong - maybe the diesel tank has to be taken out of the car?
How is it done in the simplest / best way?
Where is the best place to detach the filler tube?
Are there more hoses / things that need to be separated before the tank can be lowered?
(except for all the connections around the tank gauge - which are already split )
Will any plastic holder break?

One connection seems to have a lock gone, does that matter? (or will it leak here in the future?)

What is the purpose of this connection?

If I have to get a new tank - Will all from Citroen C5 fit? or is it different petrol / diesel as well as different generations and different which model of car?
What do I need? Item number?

[Paul-R]

The fuel tank is plastic and so it distorts a little when full with fuel. As a result it's difficult/impossible to tighten the big locking ring and get a decent seal. It's best to have a near empty tank when fitting the ring and seal. In addition there is a special tool to tighten up the locking ring which applies force equally around the ring. This will also help with sealing.

https://duckduckgo.com/?q=psa+fuel+tank ... ave&ia=web

I would think the loose connector might be the source of the leak. It should be pushed on so that connector is over the raised ring.