J.w Electrical & Property Maintenance

You would be looking for a flapper valve cap or you could replace the while unit to a dual flush system as then no longer produce these systems.

Yes silicone can be used to re seal your sink aslong as it is nice clean and the area is prepared properly before re installing.

This would need to be disconnected after water supply is disconnected and emptied so that a new valve or ptfe take can be applied to seal threads l.

Grinding noise in pipes from main supply up to loft storage tank this could possibly caused by sediment build up in the bottom of your tank and once the tank is empty the mains water will try and refill this causing the sediment to be thrown around inside of the tank possibly causing the noise you can hear.

This could be cause by excessive water and flow speed what we could do is a pressure test to see what's going on.