prove this theory wrong?

It is really hard to say if it will work or not. The reason is that the surface tension of the water might not be enough. The concept is to create a gradient of pressure, but we also need a way to preserve it. In the case of the straw the surface tension of the water is enough to preserve the gradient of pressure, but I do not know if it will work for a bigger system. My guess is that it will not work.

Anyway you can try the following experiment

Take a bottle of water and cut out the bottom of it. Then introduce the bottle in a bowl of water with the cap open until only tip of the bottle is outside of the water. Then suck water in and try to close the cap. I am assuming that you can close the cap fast enough there will be enough pressure to keep the water from failing down. If it do not work it maybe because the bottle is bigger than the straw and the surface tension of the water is not enough to preserve the pressure gradient in something that thick. For example if it was working until you removed the bottle from the bowl then it might be evidence that you pool cannot be made.

Assuming that it worked

Now we want to know if you can swim in the water. The idea will be to introduce something that is bigger than the cap of the bottle and has a similar density than the water. I would try some cooked pasta thick enough to would not go through the bottle or maybe a piece of ice. Then you repeat the experiment trapping the pasta or the ice inside the bottle. Then you can imagine that you are it and check what would happen if you try to swim in your pool.

If you do the experiment, please let me know the results.

I dont see it working you have to get a straw big enough that would be like a swimming pool it will take time for that and you would have to have a power enough to suck all the water out and plug big enough to stop it ?

Well, first you could possibly do that, then if you try swimming upside down you would most likely fall out, or even drown. Simply, the theory is wrong,

If I'm not mistaken, I think you should be able to swim perfectly fine upside down without going through the pains of acquiring such equipment.

It's wrong.