Okay, you wanted to do your part in conserving water, so you bought a Caroma toilet, that expensive Australian brand that's does both 3L and 6L flushes. And then you discovered that the toilet bowl design is really badly flawed. When you flush, a bit of the contents of the bowl go flying into air and coat the underside of the lid of the toilet if you have the lid down, and we really don't want to consider what's happening if the lid is up.
You can see the cause of the problem in the attached picture. When you flush, water from the tank jets out along the underside of the rim at fairly high pressure from both sides. When the two streams collide, they change direction and ARC through the air to the backside of the toilet, where they lose their velocity with a great deal of violence. This splashes the toilet bowl contents into the air. In addition to being a mess to clean up, this poorly directed flow does very little to keep the bowl clean and that spray is distinctly unsanitary, particularly if your digestive system is a bit on the runny side (my fellow vegetarians are probably nodding knowingly).
Step 1: The desired flow
What we'd really like to have happen is the two jets of water spiral along side the surface of the tank in the same direction. Of course to do that, we'd need a device (the green shape in the attached picture) that would completely reverse the direction of one stream, and gently alter the direction of the other stream.
Step 2: Constructing the flow modification device
My flow modification device is cut from a gardener's kneeling pad. It's stiff, closed cell foam and cost about $5 at a local hardware. It just happens be the perfect thickness to fit snugly inside the lip of the bowl. Note: the lip of the bowl is wider on the sides than at the front.
I used a pair of cheap scissors to cut the the fin shaped piece below.