I have a clear fuel line connected to a short copper tube that is soldered to a copper end cap. It was an easy way to get fuel into a pump and it was working well. Today I noticed a discoloration of the gas in the fuel line close the copper. It turned kind of reddish in less than 24 hours of exposure. I took the cap off and didn't notice any reaction on the copper, but the gas inside was discolored. I have read mixed opinions about copper reacting with gasoline. Is this a known problem or is it something else like some residue on the copper end cap? I'm testing another end cap to see if anything happens, but it has me concerned.