First, the drawing problem. I did mine in power point, and then copied the picture into Paint. Just about every computer has that program installed on their computer when they buy it.
If you have paint, once you copy your picture into it, select "Image", then "Attributes". Change your units to pixels. That shows you the size of your picture.
Mine was about 716x496. Not wishing to spend a lot of time on this, I just shrunk it by half. Select "Image", then "Stretch/Skew". 'Stretch' both the horizontal and the vertical by 50%. The result is a 358x248 picture, small enough to past on the board. The picture probably has to be saved as a GIF or the file size will be too big (this might mess up your colors, but that's life).
Second, I think your general idea with the bucket might be close (it's always hard to visualize your explanation). If you look at the bowling ball picture, you could reverse the angle of the see-saw (empty tank lower - full tank higher) and hang an empty bucket or series of buckets from the high side. You'd need two outlets from the full tank. One to fill the buckets - as the bucket became full and began to lower the see-saw, the next bucket would drop low enough to be filled, and so on. The other outlet is connected to a pipe or hose so the water can be drawn through by the lowering pressure on the empty tank.
If the water will flow out of the full tank into the bucket(s), it's going to lower the pressure, forcing the piston down (plus the force of the extra weight in the bucket from the water), but getting the water to start flowing out of the outlet in the first place might be a problem - something has to displace the volume of the water leaving the outlet. I'm thinking at least some air will run into the outlet to get the water started, and once the whole piston scheme has been set into motion, the water flow increases and you have no further problems.
It might just be better to leave the top of the full tank open and rely solely on the piston creating a low pressure in the empty tank.
Edit: Obviously, both tanks are going to have to be elevated so the buckets have room to lower.