I opened. And also let the water flows out from there. Still the same.

But I have yet to try to off the stop and open other faucet or shower drain to let all water out?

How to replace? Can't take it out.
Yes, it is concealed and I have no way to open the whole without ketuk the wall first.

What is the effective way to flush out the air inside?

The vibration is until another toilet's pipe and the sound is very loud like wuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu

thanks for this video

let me find out on how to "kepik" the thing to take off the whole

it looks like no kaki tangan to kepik because the tiles sangkut