Vapour Check Valve

[NSFIAT]

I'm hoping someone can help out, or even point me in the right direction on this one!

I pulled the gas tank on my '81 last year due to heavy rust. I'm replacing as many lines as I can and have picked up a new filter & pump. I was surprised at how much rust was in there and it definitely wasn't salvageable. I've picked up a new tank and have continued the process of replacing other components of the fuel system. Yesterday it was the vapour lines and the one way check valve that sits just outside of the tank (I had to turn to Google to figure out what it was).

When I removed the green vapour lines from either side I noticed a thick, grey grease that was starting to plug up the lines and the valve itself. I haven't encountered this elsewhere and was wondering if this accumulation is normal after an extended period of time or if I should be looking for the root cause elsewhere? After cleaning it out the valve seems to be ok - very little air is able to move from the direction of the tank to the front of the car, while lots of air is above to move from the front of the car towards the tank.

I've only run the car for about a year - one of the first things I noticed was a crazy amount of negative pressure on the tank. Would this be related?

[baltobernie]

Yes. You are heading in the right direction; as long as the one-way valve is operating as intended, you can use it.

[NSFIAT]

Perfect - thank you for the input! I finally have the car running and haven't noticed any negative pressure on the tank since cleaning things out.