In stumped. Not easy to do.
 

I just cleaned out the 68's gas tank ..lots of crap but this is perplexing. A few large clumps of non metallic crap. Could it be the remnants of the copper float. Nuts were shiney when put in the tank.

Re: In stumped. Not easy to do.
 

Tank came out great

Re: In stumped. Not easy to do.
 

No idea on the gunk. Are you going to use a sealer to coat the inside of the tank?

Re: In stumped. Not easy to do.
 

Maybe the remnants of a sock for the fuel pick up?

Re: In stumped. Not easy to do.
 

With the gas caps located so conveniently, there is absolutely no telling. Kids dropping rocks, toys, cat poop (yup) in these old fuel tanks isn't rare at all.

I'd go one further, and put a double handfull of small screws, nuts and bolts and some ATF in there, hang the tank from a rope at it's balance point, then slosh everything back and forth. The smaller hardware will get into the corners better than mid-size nuts, and ATF is a decent cleaner.

Re: In stumped. Not easy to do.
 

I used phosphorus acid to get the rust out with the nuts to agitate it. Should have a nice phosfate coating on the tank. Not going to coat it.

Re: In stumped. Not easy to do.
 

It could be MY old socks, I have a few solo artists arcin around here... :)
Just my 2c, but while you've gone to the trouble to clean it, the inner coating goes a long way to keeping ANYthing that didn't get flushed from coming loose and clogging the new filter sock. it will take time to clog, but it would take a lot longer to clog with an inner seal coat - and they are very easy to apply, much less work than the cleaners, assuming you still have the tank out (pour in, roll over a time or two, let dry, repeat and let dry lying on the other big side the 2nd time for a pretty even inner coat). I recently did this to my 59 MF50 tractor's tank and it seemed to make quite a clean surface that sealed in all the crap that looked like it could come loose over time after I cleaned it and before I coated it. Just a thought, either way, BIG improvement. I guess I'll throw away one of my mis-matched socks now.

Re: In stumped. Not easy to do.
 

I think Joe Dirt figured it all out for us. It's space poopy

Re: In stumped. Not easy to do.
 

Well its definitely organic. Dissolves completely in water. Had to rinse the tank 6 times with hot water. Phosphate coating held up no flash rust. Nothing in there anymore. I did flush it with isopropyl alcohol to dry it out .