Hi James,
I'm a mechanical engineer with over 15 years experience in designing, modeling, prototyping and effective manufacturing of different products, ranging from consumer goods to alternative energy systems.
I could design and manufacture the prototype of the valve and the egg (you'll have to give me the dimensions of the egg and prefered material), and based on the prototyping results (you know that prototyping is more expensive then mass production, and also is required in order to check the design and the functionality), I will give you the price for larger quantity.
Anyway I have to tell you that the pressure you indicate is very low (6kPa=0.06bar) which mean that will that the atmospheric pressure will prevent the water to flow from the egg.
If ther is any tricky issue, you'll have to tell me.
First at all, I'll have to make a 3D(virtual) prototype of this instalation, which to show how it works.
Second I'll have to test the concept into an improvized vessel(where to have just 6kPa pressure).
After this I'll do the prototype.