I've got a spare fuel tank from a '77.  I've had it for a while and been meaning to restore it.  It was pretty ugly from sitting for who knows how long but salvageable.  Last summer I had it hot tanked to get rid of the crud inside and after being in the hot tank for 3-4 days, I was getting ready to POR 15 the inside.  It turns out that both the return and feed lines inside the tank were clogged. I tried running different gauge wires down the lines with no success.  CLR, Acid couldn't get in far enough to get to the blockage.  Air compressor didn't work either.  I had to put the project on hold.

Now I'm back at it.  I cut a hole in the top of the tank for easier access to the lines.  I figured the best way to get to the blockage was to cut the lines, which I did.  Success!  They were clogged all the way down by the baffle tube. Got them free flowing again.

My question is how best to repair the cut lines.  As you can see from the pictures, My thinking is to put a sleeve of slightly larger fuel line over the slice in the lines. What would be the best way to attach/adhere the sleeves?  Brazing will be tricky in the confined quarters of the tank. Would something like a JB weld  or something similar work in that situation?  I would think there would be some pressure there.

Of course the tank will be re-cleaned and lined when I get these fixed.

I've put a sleeve on the bottom return line to show what I'm trying to convey.

 

For the thin line you could perhaps use those links that are used in brake lines. You could check if larger diameters are available..

 slide some rubber fuel line and a couple of hose clamps over the cut and clamp them down.

Compression fittings.  

 

http://www.autozone.com/fittings-and-hose-line-connectors/compression-fitting  

How co-incidental is this. I spent this week resurrecting the 10-15 year dormant fuel system on a 78. Every section of the hardlines, including the fuel rail, was plugged including the fuel pump.  A lot of the old fuel sludge blew out with compressed air, but no such luck on the fuel tank itself. The tank had 40 litres of the smelliest grossest sludgy crap I've ever dealt with.

I tried the poke it with a wire method with no luck, then I resorted to petro-chemicals (I used Laquer thinner) to melt the stubborn blockage in the return line. I hooked up a 3-4 foot chuck of 5/16 rubber fuel line to the return tube, and hung it vertically up beside the rear fender to get it higher than the tank. I then filled the hose with laquer thinner and gave it a couple of hours to work on the crud it was now in contact with. 

I tipped the hose down into a low pan and out poured first clear laquer thinner then browner and browner then dark rust/crud/sludge. I repeated this process one more time, got more crap out, then applied compressed air the line and PHOOOMMM blew out the last of the crap.  The old Z now purrs like a kitten.  Required a new fuel pump too. 

I wish chemicals and air had worked but the blockage was so far down I don't believe they could reach, at least none of the others did.  My patience had worn off anyway so I went for the Nuclear option .

I do like the idea of compression fittings or flare nuts.  Sometimes my brain is broke and I start to over think simple solutions.  That's why this is a great group of folks here. Y'all help keep me in line. Thanks! 

Just to finish off this thread, I wound up using ksechler's suggestion and used compression unions. The reason being that I will use a phosphoric acid wash to prep for POR 15 tank sealer and I don't think rubber and clamps would hold up long term.  For the curious, the bottom return line is a 5/16".  The top feed line is a definite 10mm, not a quick and easy find for a compression union.

Tank looks nice inside now!

Looks good!