How do you clean a radiator overflow tank?

[David Rubie <drubie@domain.elided>]

The radiator overflow tank on my Alfetta turned into
the Hotel California of radiator overflow tanks
yesterday (i.e. coolant checks in but can't check out).

Inspection revealed a blocked hose and nipple on the tank,
full of gooey/crusty/powdery stuff.  I often wondered why
I couldn't check the coolant level by eye.  Turns out that
the entire bottle wasn't simply opaque, it was covered
internally with a layer of crust that suddenly
decided to flake off in big chunks yesterday, blocking
the hose.  It's possibly from an ancient head gasket
failure but it mostly looks like what coolant turns into
when it dries out (i.e. white powdery crust).

I cleaned it out as best I could (flush with water/some mild
solvents) then scraped as much out as I could with a wire, but there's
still plenty of it stuck on the sides of the tank.

How do I clean it out?  What sort of solvent is the
best for this gunk?

dave.

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