A Bug's Life

I have a stack of cut-down index cards on the desk, on which I note down Things To Do. Later I will separate them into ones with urgent deadlines, and ones which would be fun if I had unlimited spare time.

I have just written down "Cute Overlord". Sadly, I am not the first to have thought of this.

We have an oil and vinegar flask that is topologically quite similar to this:
( photo of someone else's cruet )
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 ;-)