AquaTweaks is a small, clientside, coremod, which aims to improve the way fluids look around non-solid blocks.
In its essence, it renders fake water into ladders, fences, signs and the likes, making them not look as derpy underwater.
Note that these changes are purely of graphical nature. Fluids will not actually flow through blocks, but simply render into them.
In addition to that, this mod allows other modders to register their blocks for tweaking. Due to the technicality of that process, I'm going to spoiler it.
There is two options. either implement the interface "blusunrize.aquatweaks.api.IAquaConnectable" in your block (this supports the @Optional annotation"), or send an IMC message.
Users of the interface get the benefit of having world and coordinates passed, allowing possible TileEntity interaction, furthermore, the get one method to check if water should render a side towards the block and another which determines if water should be rendered into the block.
IMC is the easy and fast method. The message must have an NBTTagCompound that that compound requires two strings "modid" and "block", which are used to grab the respective block via GameRegistry.findBlock();
You can also add an integer under the key of "meta" if you only want a certain metadata of the block to AquaTweaks. Without meta, it will default to 32767, the universal wildcard value for damage.
IMC messages are sent to the ModID "AquaTweaks".