Making an instructable for this was an afterthought, so I apologize for not having step-by-step photos.
This summer I decided to try and reduce our water usage in our toilets.
We have three 1.6Gpf / 6.0Lpf toilets throughout the house.
My first thought was to use the old 1/2 gallon milk jug in the tank trick. Upon opening the tank, the space was so small, I knew this wasn't going to work.
I shortly considered using a couple of bricks, which might have fit okay, but I really wanted to reduce the water usage more than that volume.
I wanted to reduce water consumption to approx 1 gallon per flush.
After studying the mechanism a bit, I thought I might be able to modify the float valve system to suit my needs.
This proved to be very easy to accomplish.
What you're trying to do is to adjust the angle of the float ball so it closes the tank fill-up valve sooner as the ball floats on the water.
This involves bending the rod and anchoring it with a lock nut.
Step 1: Turn Off the Water to the Toilet Tank.
Step 2: Unscrew the Float Ball From the Metal Rod
Be careful with this step, as you don't want to damage the plastic valve assembly.
Most likely the treads will be corroded a bit and it might be a little stubborn, so use a pair of pliers to grab the rod while you unscrew the ball.
Step 3: Screw the Metal Rod Completely Into the Plastic Valve Assembly
But since we're dealing with plastic, simply cranking down the lock nut to prevent the rod from rotating might damage the threaded plastic valve assembly.
So what you're doing in this step is threading the rod as far as it will go, that way when the lock nut is screwed on, the rod will be less likely to loosen up and rotate in either direction over time.
You may be able to just skip this step if your lock nut will hold the rod whether it's screwed in all the way or not. This will also allow you to rotate the rod for minor adjustments once the ball is reinstalled.
Again, the threads may be corroded. So be careful not to damage the plastic valve assembly.
Use a pair of pliers to gently assist and work the threads loose.
Screw the rod in as far as it will go until it's snug, but don't over do it - remember they're just plastic threads.
Step 4: Mark the Rod With a Sharpie
Since we will be bending an angle in the rod, we need to mark the top of the rod with a short reference line down it's length so we can bend the rod in the proper direction once it is screwed all the way onto the valve assembly.
This is where you'll need to do some trial fitting for clearance.
The rod will be bent about 10-15 degrees downward. This should give you an idea of about where the ball will ride when connected to the end of the rod.
Make sure you plan to bend the rod so the ball will not rub against any of the toilet innards.
Put a mark on the rod about where you think the apex of the bend should be.
Step 5: Bend the Rod
Be careful, the rod is relatively soft metal.
It's always easier to bend it a little bit at a time, than to unbend it if you've gone too far. (ask me how I know)
As you work, stop and screw the ball onto the end and test fit everything to verify the angle you want.
Please keep in mind, that whatever angle you choose to bend the rod, it will still need clearance to be spun back into the valve assembly. If you bend it to much, it may hit the side of the tank when you go to screw it back in.
Step 6: Install the Lock Nut
I can't remember what size mine was, and they may vary between tanks anyway.
Make sure you use a nylon lock nut for this instructable.
When I first had this idea, I used a regular nut and everything seemed to work fine for a few weeks until I heard the toilet running. The nut had loosened and the rod had rotated so that it was now in a "V" position...which was actually using more water than before.
I threaded my lock nut onto the rod with the nylon insert facing away from the threaded plastic valve assembly. I figured the fatter end of the nut would have the most friction against the valve assembly in this direction.
Threading the nut nylon end first onto the rod can be tricky. It helps to flip the nut around and run it onto the threads "normally" once or twice to "cut" some threads into the nylon insert.
Step 7: Reinstall the Rod and Float Ball
If you've bent your angle correctly, you should be able to thread the rod on until it's snug and the ball should have clearance to freely move up and down once it's threaded back on.
Screw on your plastic float ball.
Before you tighten the lock nut turn the water back on and let the tank fill.
Now you can make any small adjustments by rotating the rod if necessary.
You can also fine tune the water cut-off by adjusting the screw on the plastic valve assembly.
Carefully tighten the lock nut against the plastic valve assembly, being careful to not allow the rod to rotate. Again, be careful not to over tighten - you can easily crack the plastic.
Step 8: Test Flush
It's also nice to notice just how much water you're saving with each flush when you look at the old watermark on the inside of the tank!
Believe it or not the toilet is now a dual-flush.
For liquids, simply press and release the flush handle like you normally would. The toilet should give you a clean flush completely evacuating any liquid in the bowl.
For solids, simply hold the handle down for a few seconds for a more complete flush which will use all the water in the tank. If one flush just doesn't cut it, you can always flush a second time.