Pressure build inside a water tank?

[saeppi]

Hey guys,
It‘s been a few years since I had my last physics class so please be kind to me. I came here to ask you about a phenomenon I recently discovered in a design of mine.
The object in question is a stand with 3 arms, holding a water tank (see pic below).
All openings are pretty tightly closed and for a few hours there‘s no water leaking. But after a while, some pressure is building which pushes water out via the bottle screw (encircled in black). Another evidence of increased pressure is that when I let water out via one of the arms it would gush out if I wait for several hours. But soon after it would calm down and water flows smoothly again. Any ideas what‘s happening here?

 

[Baluncore]

Welcome to PF.

How do you fill and close the reservoir?
Please give us a link to the product on the web.
If you fill it with cold water, that will warm over time, and the air will expand, building up pressure.

 

[saeppi]

If you fill it with cold water, that will warm over time, and the air will expand, building up pressure.

Hi Baluncore,
Thanks, I think you‘re on point. The pressure build up happens overnight when we turn our AC off and the room warms up. How could I potentially counter that? Small hole at the top of the glass bottle?

 

[Baluncore]

How could I potentially counter that? Small hole at the top of the glass bottle?

I have never seen one before, so I do not know how it is built or operated.

How can water drain out if air cannot get back in?
As water is removed, a reverse flow of air would need to enter and bubble up to the surface, or a partial vacuum will form, that will prevent it dispensing.

A 1 mm hole in the top of the reservoir might be drilled, and could have an air permeable plug, to prevent dust entering.