A Bug's Life

We have an oil and vinegar flask that is topologically quite similar to this:



Ours is shaped more like the conical flasks used in laboratories; there is a spout on the side for the oil, and the neck at the top leads to a smaller cone for the vinegar.

The oil had got a bit old, so I tried to clean the flask today. My problem is that the oil has formed small solid blobs on the bottom of the flask. I can't get a bottle brush or anything inside to clean it with; I have had some success with dishwashing liquid and very hot water and shaking, but this has left a thin sprinkling of oil on the inside and the flask looks rather speckly and traps bubbles.

I have remissly forgotten my school chemistry - what might I have around the house that I could soak the flask in, to remove the oil and leave the surfaces clean so they dry clear, and won't poison me when I refill the flask?
Acid? Alcohol? Bleach?

EDIT: Thanks, cookwitch, lemon juice worked a treat to bring up the sparkle!

Thanks, everyone else: I have just tried peppercorns as agitators, but either they're not dense enough or the oil remnant layer has turned into some sort of polymer and I'd need mini-caltraps to break into it...

I don't have bicarb, and didn't think cornflour or custard powder would have the same effect!

I shall continue with hot water efforts, possibly putting in some hot oil and standing the flask in a bath of hot water. I think I need an ultrasound bath ;-) Or magnetic stirrers with little brushes on ;-)