Some of my T-shirts had acquired that mildew smell and it wasn’t washing out. Left them to soak in a bucket of water with a cup of vinegar in it. Washed again and hey presto - back to smelling fresh.
Likewise, if your washing machine is Pongy do a (empty) hot wash with a bottle of white vinegar in.
If you want it really clean, open the bottle and pour the contents in instead.
(I suppose I could have just re-typed the first bit but I haven’t finished my poo yet).
Some of my T-shirts had acquired that mildew smell and it wasn’t washing out. Left them to soak in a bucket of water with a cup of vinegar in it. Washed again and hey presto - back to smelling fresh.
This felt like a very middle aged win.