Hi everyone,
I have a galvanised tank as shown below, and I understand from the useful postings here is that it is a non-bladder tank.

It's been working fine since we moved into this house two years ago. Although the pressure is not exactly fantastic. Recently, during my absence overseas, my wife hired a plumber to fix a problem with the filter. He moved the filter housing which was on the pump side of the tank and put it on the other (pressurised) side of the tank. Since then, we've been having frequent problems with air coming out of the faucets. If I turn the pump off and drain the tank, then re-fill it, all works fine but only for a week or two before the problem comes back.
I have read another earlier thread here about air in the pipes, but couldn't quite follow the advise about the pipe connections for avoiding the air problem. So I wonder if someone could kindly describe this to me. Many thanks in advance for this very educational site!

Here are some more pics of the tank that might be useful:


Best regards,