Cleaning a flask that makes tea taste weird

[Hullabalooo]

I do a job once a week where they don't have a kitchen so I bring my own tea in a flask. Except the tea coming out of the flask is starting to taste really musty and odd.

I've been cleaning flask with boiling water and so on but no change. Any tips to rescue my morning cuppa? The flask is stainless steel and only about a year old so don't know why it's tasting like that.

Any ideas?

Steam clean it?

I had this years ago when I had to make my dads tea for his lunch at work. It sounds weird but putting cheap white bread in overnight helped (possibly some toxic additive bread had in the 80s absorbed the smell!) or maybe bicarbonate of soda?

Baking soda and vinegar

We use Milton on water bottles. Not sure about a metal thermos.
Mum's hot lemon water does a very good job of removing DHs builders tea stains when she visits, so that might be worth trying.
Vinegar and bicarb sounds good.

Make sure the lid is well cleaned too.

Ooh thanks you lot!

I boil mine in a saucepan

Flasks tend to make tea taste weird, I was always taught to carry the milk separately, it's the milk sitting in the hot tea that kind of affects it. Worth a try anyway. If you take a small water bottle with just enough milk for the day you shouldn't have an problem with the milk going off.

Once it's clean, don't store it with the stopper in.

Bicarb, vinegar and hot water steeped in the flask overnight sorts DP's out.

I'm trying sterodent this morning!