I've cleaned out a rusty tank before using kerosene and road gravel. With the tank out, you rock the tank back and forth with some oomph! The sharp gravel cuts pretty well, and the kerosene is the washing/cleaning solvent.

 

Yep, 3/4 minus does a good job on a car gas tank!
Whatever you use, make sure you clean it well, or you'll be pushing more junk through the system later!

 

Once again, looks like you guys nailed it! Took me a while to get to it, but filled bottle with fuel directly from pump, and it was filled with sediment. I''m going to replace fuel tank, sending unit & fuel filter. Can fuel lines be flushed, or should they be replaced? Thanks again! I think this willl solve the problem

 

Fuel lines can be flushed, and I've even pulled a patch through them to wipe them out. Unplug both ends and blow all the fuel from the line, then get your shop vac and tape the hose down with duct tape to one end. Turn the vac on and tie a knot in a piece of heavy twine, then feed it in as the vacuum pulls it. Once the line i through you can tie a small piece of cloth that fits inside the tubing to the line and then go to the other end and pull it through. You'll have a nice clean line when you're done!

 

Not to mention fuel line is cheap is you mess one up

 

Inline Tube in Macomb, Michigan makes a set of either stock material or stainless steel. They're reasonable (around $175 for SS) and are factory fit. I believe they have them stocked normally. They're good option if you want to make sure you have clean lines.