malypython, what you describe is two different problems:
1) water flows in your nostrils when being face up (it happens to me, too, and is quite common!)
2) you have problems equalizing your ears without a mask
Lets talk of first problem, equalization of pressure in ears, mask, and other cavities in your skull would require a whole book for being discussed properly.
It is true that some people can stay underwater facing up without any apparent problem, and they say that water does not flow in. But they are a minority!
Most other people, as you (and me), have larger nostrils, wide-open nasal duct, and water flows in easily just for gravity. It floods completely the nasal cavity, and this is quite unpleasant. It can easily go pass the soft palate and come into the mouth. People who don't suffer of this problem simply do not understand it!
There are very few solutions to this: squeeze your nose with fingers when facing up, use a nose pinch, insert wax in your nostrils (this is what athletes of synchronized swimming usually do).
If you nasal cavity has been flooded by water, then it is a quite bad idea to equalize you ears: you open the Eustachean tubes, water will flood also the medium ear, and it is very easy that this will cause a lot of medical problems.
So I simply recommend you to avoid that water floods your nasal cavity. If your nostrils are like my ones, exhaling is not enough, you must close them with fingers or with a a nose pinch.
But the final point is another: why do you want to swim underwater without mask or nose pinch in a face-up position?
1) water flows in your nostrils when being face up (it happens to me, too, and is quite common!)
2) you have problems equalizing your ears without a mask
Lets talk of first problem, equalization of pressure in ears, mask, and other cavities in your skull would require a whole book for being discussed properly.
It is true that some people can stay underwater facing up without any apparent problem, and they say that water does not flow in. But they are a minority!
Most other people, as you (and me), have larger nostrils, wide-open nasal duct, and water flows in easily just for gravity. It floods completely the nasal cavity, and this is quite unpleasant. It can easily go pass the soft palate and come into the mouth. People who don't suffer of this problem simply do not understand it!
There are very few solutions to this: squeeze your nose with fingers when facing up, use a nose pinch, insert wax in your nostrils (this is what athletes of synchronized swimming usually do).
If you nasal cavity has been flooded by water, then it is a quite bad idea to equalize you ears: you open the Eustachean tubes, water will flood also the medium ear, and it is very easy that this will cause a lot of medical problems.
So I simply recommend you to avoid that water floods your nasal cavity. If your nostrils are like my ones, exhaling is not enough, you must close them with fingers or with a a nose pinch.
But the final point is another: why do you want to swim underwater without mask or nose pinch in a face-up position?