If you have an older toilet, a faulty fill valve can cause it to leak, wasting water and money. Generally, your best bet is to replace it. It won't take much time. If you follow these steps
Step #1 Remove toilet tank lid and turn off the water supply
Step # 2 Flush the toilet handle and use a large sponge to remove all water from the tank.
Step # 3 Disconnect the water supply nut that connects to the fill valve using a pair of channel lock pliers
Step # 4 Remove the large plastic nut that holds the fill valve to the toilet and pull out old fill valve
Step # 5 Open new fill valve box and install rubbber washer on bottom of fill valve. Then insert the new Fluidmaster # 400 fill valve in the same opening .
Step # 6 Install the new large nut to fasten the fill valve using you pliers.
Step # 7 Install refill tube into over flow pipe wuth clip provided
Step # 8 Install teflon paste on the old supply tube and connect water suplly to the new fill,valve
Step # 9 Turn on water supply and adjust the water level if required
Check for leaks and remember to call JP Plumbing for your other plumbing needs.