Fuel tank vent?
 

The other day when I fueled up my car I had a large rush of air when removing the gas cap. Then I also had a hard time fueling the tank because it kept shutting the pump off. So I think it may not be venting properly. I checked to make sure it was not imploding and that seems fine. I want to check the valve but I want to make sure that I wont get soaked with gas taking it off. Also want to make sure this is it. IMG_20170723_170717.jpg Photo by hanly2 | Photobucket

It "MIGHT" be a picture of a FT Vent
 

BUT WE"LL NEVER KNOW UNLESS SOMEONE WITH THE SAME:
MAKE?
MODEL?
YEAR?
AS YOUR CHASSIS "RECOGNIZES" IT !!!

I'll go out on a Very slender twig of a Limb and state that what I See
MIGHT be a Fuel Tank fuel line (Delivery/Return) line WITH ZOME other
device crowding it in the Picture.

Haha I'll give you 3/4 it's obviously a Mercedes. It's a w124 300e 1990

1999 E300 has rust that developed 6 years ago on the inside fuel fill cap.

Any ideas or help solving and rectifying this situation that causes the rust?

Rust = s WATER inside Diesel Fuel system
 

BAD !

'Nutcase that I am I run the Diesel through an Aircraft Type Water Separator
Funnel Before it Hits the Tank !

1. Fuel Supplier that has high volume has (Zometimes) less suspended Water
in Their Diesel.
2. Starbrite's "Startron" (An Enzymatic) will help remove Water SAFELY !
2.a ALWAYS READ ALL LITERATURE THAT COMES WITH DIESEL ADDITIVES !
2.b Zome Additives that tout Water removal USE ALCOHOL (VERY,VERY BAD).
3. A Full Tank Helps by not allowing Heat/Cooling Cycles to Condensate
WATER on the Tank Walls (Which ends up in YOUR PUMP [That's I.P.]
and Injectors.)
4. Remember the Diesel in our cars is Constantly recycled by the Fuel return
System,so WATER NEVER VOLUNTARILY "GOES AWAY".
5. A Nice Big Fat Industrial sized Water Separating Fuel Filter WITH DRAIN
Will ALMOST provide perfect protection. I'm not gonna say Cat or Racor
But you get the Idea! Having a Water sensor on the FF Is a PLUS !
6. No Water IN Fuel Means Fungus/Biologicals can't get a Grip!

VW has a W. Sep FF system on the Old Golf/Jettas that would fit the bill.

Me (?) Cat Or Racor plumbed in between the (Clear) Primary [The Little One] and the Lift Pump on the side of the I.P.
[2 Microns]
Which makes the Secondary ["Spin on"] filter just a "Place Holder" in the
distribution system. [Too Much Hassel trying to fit a "Monster" on the
Spin on Filter Head SPACE LIMITATIONS] I do believe it Supplanted the
Windshield Washer Bottle that was next to the Oil Filter Housing.