Ways to clean a stainless steel flask inside thick with a coating of milky tea

[Gattopardo]

Been cleaning two stainless steel flasks.

One took sterident tablets over night with hot water, bicarb of soda and hot water over night, and then sour salt (acetic acid) hot water over night to clean one. Even then the coating didn't dissolve but peel off.  Number two flask so far has had strident and bicarb treatment but these haven't worked.

Anything else to try to clean the inside.

[rogerzilla]

Have you used a bottle brush?

Do NOT use washing powder (which is excellent on teapots).  It tends to get into the seams and taints the next 5-10 flasks of tea.

[yoav]

What you need is something called Astonish Clean and Revive. Add a spoonful to a flask filled with boiling water and leave for two hours, before rinsing it out.

[bikepacker]

What you need is something called Astonish Clean and Revive. Add a spoonful to a flask filled with boiling water and leave for two hours, before rinsing it out.

+1

[Kim]

Bung a load of bleach in there and run away?

[Mrs Pingu]

Dunno what's in the Astonish stuff but I would suggest a soak with a warm solution of washing soda (sodium carbonate) which is quite good at breaking down fatty protein-y type stuff.

[T42]

sodium carbonate

Which you can obtain by heating bicarb in an oven at 120°C for half an hour. Or was it an hour?

[Paul]

Have you used a bottle brush?

I love this one:
https://www.ikea.com/gb/en/p/medelvag-bottle-brush-white-40385067/

[sparklyfish]

I tried leaving to soak with Milton in a similar situation (for a couple of days I think). It damaged the flask such that my nice vacuum flask was no longer vacuumy. Cold tea is bleurgh!

[Mrs Pingu]

Yeah bleach is corrosive to metals so won't do it a lot of good.

[Mrs Pingu]

What you need is something called Astonish Clean and Revive. Add a spoonful to a flask filled with boiling water and leave for two hours, before rinsing it out.

Well, because I'm a nosy chemist I looked that up and it's just sodium carbonate, or soda crystals

The Astonish stuff is £3.50 for 350g, while the Homecare Soda Crystals are a mere £2 for a whole kilo, leaving plenty to chuck in the washing machine or down a drain once in a while

[yoav]

TBF, I bought it in Poundland for £1 but I take your point.

[Gattopardo]

As I had soda crystals I stuck a tablespoon in with boiling water and a hour later the inner coating of yuk came off when I poured the stuff out in to the sink.

Have you used a bottle brush?

Tried a dishwasher brush and that did nothing.  Nor the green scourer.

[Mrs Pingu]

yay!

[MattH]

To be honest, the only real answer is to only put black coffee in flasks.
Unless it's a hip flask, in which case something stronger may be appropriate.

Milky drinks from flasks are just wrong.

[Flite]

To be honest, the only real answer is to only put black coffee in flasks.

Agreed. Drinks with milk added just taste stewed.
Separate milk in a little bottle in the same small box as my frozen cheese scone.
By the time I want them, the scone has thawed but kept the milk cold.
WinWin.

[PhilO]

I've had some success by simply putting a bit of sand in the flask with some water and shaking it vigorously.