You need to replace tank valve.
See photo of the product:http://salestores.com/fluidmas.html
Buy this product at hardware store.
Turn off water to toilet.
Flush toilet to empty water from tank.
Under the tank, the tank valve is held with two nuts.
Nut1 seals water line to the valve.
Nut2 seals valve to the tank.
Loosen nut1 and it drops down. You can use same nut for new valve, or use new one that comes with product.
Notice there is a beveled washer stuck in bottom of valve, or stuck inside nut1. Your new valve will have a new beveled washer.
Loosen nut2 and valve come loose and can be lifted out.
When you lift up valve, remaining water will run onto floor so have a pan and towel ready.
Notice on bottom of valve is a rubber washer. This washer seals the valve and tank together so water will not leak.
New valve comes with 2 washers > big one and small one. They are usually attached together, small one inside bigger one, and you have to tear them apart.
Clean opening of sand and dirt.
Supply pipe is sticking up.
Put nut1 and small beveled washer onto the supply pipe, with flat side of washer facing downward and rounded side facing up toward tank.
Put bigger washer on bottom of new valve. Flat part of washer goes to valve, beveled part of washer faces downward to tank.
Set valve in place and notice how washer covers the hole.
Put nut2 on bottom of valve and tighten. As you tighten the nut, valve will rotate inside tank. Make sure float and parts can move freely.
The valve doesn't have to be super tight to seal. Just tighten ia reasonable amount, and you can tighten more later if needed.
Now attach nut1 to bottom of new valve and this will seal supply line going into tank.
This nut has to be fairly tight.
Turn water on.
Valve has adjustments for selecting height of water inside tank.
Use paper towel on bottom of valve to check for leaks.
Leave catch pan under new valve for couple days to make sure there is no dripping.
If water is seeping, then tighten nut1 or nut2 a bit more.
Sometimes the shut off start leaking. Open shut off all the way to see if this solves problem.
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