Cleaning an R&T A1250 toilet fill valve
I have an R&amp;T A1260, which looks very similar. This is how you open it up. At the bottom, you'll see a little pull tab. Pulling on it will remove a filter.



The top has a blue cap that can be lifted by the two protrusions.


There is a horizontal pin here that you can remove with a pair of needlenose pliers by simply pulling it out.


This frees up the water level adjustment arm, which you can set off to the side. Now you want to rotate the whole top part so that the groove that held the adjustment arm rotates to align with the green overflow tube, which is about 15° counterclockwise. Take a pair of standard (not needlenose) pliers and grip the two raised walls that contained the adjustment arm, push down into the shaft and turn. This unlocks the top of the mechanism so you can just remove it.




With your needlenose pliers, grab the inner plunger and lift it out.



When it stops, gently tug on it with some more force. There are some O-rings that give some resistance but you should be able to overcome it easily. This pops the whole plunger out, finally exposing the inner chamber of the shaft.



In my case, I found a piece of metal that had blocked the inlet. It's otherwise in good shape, except perhaps for the worn gasket at the bottom. Yes you could replace the whole thing, but if you have the patience to disassemble and clean it out, you could probably get a few more years of life out of it.