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By stinkwheel
White vinegar works well for lightly rusted metal. Followed by a rinse out and a dry. It will flash-rust again quite quickly though.

For looser/flaky rust, a handful of nuts loosely threaded on string in the tank with some petrol added then swirled about will knock the rough bits off. Follow up with plenty of rinsing. The nuts are on a string so you can fish them out again. In the old days people used to quarter fill the tank, throw in a handful of stones, wrap it in a duvet then put it in a cement mixer for half an hour. Modern tanks are much thinner steel though so I wouldn't recommend it.

Be aware, it's not unusual to find pinhole leaks appear after de-rusting a tank.

For a really good, permanent fix for a rusty tank, I can highly recommend the POR15 system. Consists of an acid flush, a degreaser flush then a paint-like resin (goes on like thick silver paint, you pour it in and swirl it round to coat the inside). This will remove loose rust, stabilise the rest, block any holes and give you a permanant, corrosion (and ethanol) resistant coating on the inside of the tank. It is vitally important you follow the instructions properly, particularly with regard to the tank being thoroughly dry before applying the coating. Works out about £50-ish to treat a motorcycle tank.

I've heard of people using POR15 as a primer on bare metal then trying to remove it with a wire-wheel and failing. It's almost like galvenising (in appearance and toughness) after it's set.
Hi from Australia , i use mollases and water to derust the motorbike tanks that come to my workshop ,
1 litre of molasses 3 litres of water , is the ratio i use to fill the tank to the top ,
leave for 1 or 2 weeks then tip on the garden as it wont hurt anything even paint ,
then rinse out with water ,
put some methylated spirits in to dry the water , then slosh a bit of diesel or oil in to stop the rusting process .
By Cov Lad
Interesting thread, I have also tried nuts and bolts, I have a cement mixer and would like to know what else to fill the tank with or did you mean jut the nuts and bolts stinkwheel?
mollases also seemed intersting, do you mean the sugar byproduct?
Sorry for bad grammar spellings - red wime has hit several spots...
By PeteF
Any old shrapnel that's not to heavy will do for the cement mixer method. Wrapping the tank in an old duvet will protect the pain job, and reposition the tank every so often.
I did this years ago on a Bantam tank with good results.

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