Your Toilet Fills Too Slowly
After the flapper closes, the toilet tank fills very slowly. Do I need to replace the inlet valve?
Come on, now... eighteen minutes is not exactly forever! Maybe an eternity, but hardly forever.
Some toilet inlet valves have an adjustment to set the length of time it takes for the tank to fill. However, if your toilet has begun to take longer to cycle, it is likely that the inlet valve is beginning to wear out, and should be replaced.
Replacement is very simple. There isn't a lot I can add to the directions on the box of the intake valve you buy, except to mention that you may want to also replace the special washer on the inlet tube. When you remove the valve from the toilet tank, look at the inlet tube. If it is chrome, there is a washer attached to the top. This washer can be carefully pried out of it's seat with a screwdriver or knife. It will look like a hose washer, but with a protrusion that sets into a flare in the top of the inlet tube. If you do not replace this washer, or the entire inlet tube, you will almost definitely have a leak at this point. Take this washer with you to the store where you buy the intake valve and get a new one. I'll warn you ahead of time that all hardware stores do not carry replacements for these special washers.
99% of the time, you will be able to reuse the inlet tube as long as you are careful not to twist it, bend it, or move it excessively when removing the old valve. When I have had to replace it, I generally use one of the plastic lines, which are easy to install and inexpensive. There are also braided stainless steel lines that have screw-on couplings on both ends. These are excellent products, virtually indestructible, and can also be used in lieu of the standard chrome replacement line.