Cleaning Out Fuel Tank

[AMXguy]

My tank has some kind of brown gunk in it that seems to be working loose and pluging my intake screen.

It's not rust, you can scrape it with a screwdriver and it's clean under the gunk.

Is there a way to clean the tank out good? I have it out of the car. I've heard muratic acid works? any other ideas?  I have to do something or get a new tank.

[Barracudadan]

Sounds like varnish in the tank did the car sit for a long time? You can get a tank from Rock auto for around $165.00 not counting the discount they offer. If your time and agravation plus whatever you spend on cleaning product and a tank sealer if your sealing it, add up to more than that I would just get a new tank. Plus it will be shiny when you look under the car! 
If you go the new tank route save your old lock ring from the sending unit they are better than the one that comes with the new tanks.
Run some fresh gas through the line and change the fuel filter after you straigten out the fueltank issue if you haven`t thought of it already.