Plastic motorcycle gas tanks porous?

[priderocks]

I am looking to buy a used trail motorcycle, like an enduro. I looked at an 86 Yamaha TTR350 today, and the white gas tank had yellowish stains on each side at the bottom of the tank. The owner said the stains were from the previous owner not quite draining the gas tank and letting it sit for a long time. The stains, he said, are because the tank is actually porous. He also said that is why gas tank graphics are perforated or have tiny slits in them so they don't bubble up from the escaping vapors. I never noticed this before. Hooda thunk it? Can anyone confirm this?

[hemiken]

What he says is true.

White tanks suffer more than any other, there are certain two stroke mixing oils that will stain a tank in a yellowish look more than others aswell.

[RaptorF229]

I remember having a motorcycle with plastic tanks that I put stickers on. Within a day the stickers were getting air bubbles under them

[340Challman]

   Tis true.

[LAA66]

I remember having a motorcycle with plastic tanks that I put stickers on. Within a day the stickers were getting air bubbles under them

 Mine is doing this right now. One week after installing the stickers. No staining after 5 years though. (it is an IMS tank.)

[RaptorF229]

I ve seen some of the stickers being perforated so that no air gets stuck