rusty tanks i fill and soak with Hydrochloric acid or brick cleaner from the hardware store which works very well.
once its clean, tip out acid
hose out with water out the tap
have a bucket or hot water ready
fill tank with hot water
swish around, then tip out
continue to work as quickly as possible.
then tip in a liter of metho and swish around and tip out.
then tip in a clean bottle of metho, swish around then tip out
then pour in a half a jar full of paint thinners, about 250-500mls will do
swish around, then pour out. paint thinners helps to dry out the tank.
then get your air gun on a compressed air line and blow the tank completley dry.
if you have done it correctly and quick enough you will be left with a bare grey metal surface with no light orange surface rust
this is the method i have used for years
with tanks with severe chunky rust inside, i may have to leave with acid soaking for several days. with some loose nuts/bolts inside and shake it around to agitate the rust. i will also tip out acid and flush out with hose, then check inside with a mirror on a stick and a torch.. if still rusty then back in goes the acid. till its clean.
usually, but not always, with tanks this bad the cleaning process creates pin holes when the rust is removed and the tank requires a liner anyway. so then i fit the RED,WHITE,BLUE tank liner kit sold/distributed by Ficeda Accessories and made in Tasmania. this will fill any pin holes. its a very good liner.
i recently did a old A10 BSA tank and it was so badly rusted. had to soak it for 2 or 3 days to get all the rust out. one of the worst ones ive seen.
