Can anyone tell me what the white plastic stick bit does at the back right of this cistern ? It literally just has a screw thread At one end but is not attached to anything and easily just screws in and out.
It appears to be the toilet version of an appendix with it having no actual purpose.
If I’m looking at the correct piece that should be screwed in to the float rising above the correct level. These days it will run into the bowl, older toilets would run out through the wall.
Adjusts height of the ball-cock which determines how much water per flush.too much and it may overflow as well....
Interesting as a lot of the time the float doesn’t quite fully rise, so get a little constant run of water unless manually lift it up the last couple of millimetres.
Should I screw it in further ( to the left as we look) or unscrew it more to the right
As water leaves the cistern during a flush, the ball cock (big blue thing) drops as the water level drops ... and this opens the valve to let fresh water into the cistern.
As the cistern fills, the ball cock (big blue thing) rises as the water level rises ... and this begins to close the valve. However, final sealing of the valve is reliant on pressure due to the rising ball cock (big blue thing) and resistance from the valve itself. Your screw thread thing should press against the cistern wall to create that resistance.
If, as appears the case, the thread is not touching the wall, there is nothing to stop the valve moving slightly (towards the cistern wall) as the water level rises and, hence, preventing the complete seal.
The valve will not leak much as it is almost closed anyway, but it is unlikely to seal fully.
Adjusts height of the ball-cock which determines how much water per flush.too much and it may overflow as well....
Interesting as a lot of the time the float doesn’t quite fully rise, so get a little constant run of water unless manually lift it up the last couple of millimetres.
Should I screw it in further ( to the left as we look) or unscrew it more to the right
OK, so this confirms that the valve is not closing fully.
The screw thread needs to touch the cistern wall.
If, as seems the case, the screw thread isn't long enough, you can (temporarily) stick something in there as well to bridge the gap between the end of the screw thread and the cistern wall. But then get yourself a new ball cock etc.
Go like-for-like if you wish ... and then it's obvious how to fit it.
Can anyone tell me what the white plastic stick bit does at the back right of this cistern ? It literally just has a screw thread At one end but is not attached to anything and easily just screws in and out. 
Comments
As the cistern fills, the ball cock (big blue thing) rises as the water level rises ... and this begins to close the valve. However, final sealing of the valve is reliant on pressure due to the rising ball cock (big blue thing) and resistance from the valve itself. Your screw thread thing should press against the cistern wall to create that resistance.
If, as appears the case, the thread is not touching the wall, there is nothing to stop the valve moving slightly (towards the cistern wall) as the water level rises and, hence, preventing the complete seal.
The valve will not leak much as it is almost closed anyway, but it is unlikely to seal fully.
Is the cistern behaving itself?
The screw thread needs to touch the cistern wall.
If, as seems the case, the screw thread isn't long enough, you can (temporarily) stick something in there as well to bridge the gap between the end of the screw thread and the cistern wall. But then get yourself a new ball cock etc.
Go like-for-like if you wish ... and then it's obvious how to fit it.
One of the best ballcock flange limiters I have ever laid eyes on.