There should be a screw at the valve end that can be screwed in and out, but it is usually so corroded that you can't. Most of the time, you just bend the rod the ball is on to adjust the water level.
Just replace the ballcock valve..
When you start to unscrew a ballcock, you are essentially loosening the connection between the ballcock and the water supply line. This allows you to either remove the ballcock for maintenance or replacement, or to adjust the float level to control the water level in the tank.
A ballcock is a ball float on the end of a lever in the water closet of a toilet. As the level of water in the closet rises, so does the floating ballcock. When the water level is high enough, the lever operates a sliding valve and the water coming into the closet is shut off.
Contrary to popular belief Crapper did not invent the the flushing toilet. He did, however, do much to increase the popularity of the toilet, and developed some important related inventions, such as the the ballcock.
Thomas Crapper invented the ballcock which was the first type of toilet thank you very much.
If you open the lid on your toilet you should see the ballcock. It is normally on the left side and has the float, that looks like a ball, attached to it. It is used to fill the water in the bowl and set the height of the water.
The water in the lower toilet is probably being siphoned out of the tank by the negative pressure caused by flushing the upper toilet. This CAN happen if the water level in the tank of the lower toilet is over the top of the ballcock. If this is the case, the tank water is being siphoned into your drinking water! Replace the ballcock with a Fluidmaster right away. If you have a small white fill valve that sits in the bottom of the tank, get rid of it. These are illegal and WILL siphon under these conditions. If the lower toilet runs AFTER the fill cycle of the upper toilet, it may be that the ballcock seals at a lower pressure, and the pressure spike when the upper toilet shuts off causes it to run a bit until the added water closes the valve a little tighter.
Your ballcock is comming on -- replace tank ball or sometimes you have to change out flush valve -- but change tank ball first and see if that will do it You hardly ever have to change flush valve -- Your ballcock is what lets water come into your tank
They have probably got air bubbles in them. It may be a worn out ballcock at a toilet.
An overflow pipe on a (toilet cistern?) will leak if the rubber disc in the ballcock slide valve needs to be replaced.
To adjust the toilet float to fix a running toilet, locate the float mechanism in the toilet tank and adjust the float arm or screw to lower the water level. This will help stop the water from continuously running.
Adjust the flow rate to a slower fill through the ballcock in the tank.