Fluid/Waterproof pipes were introduced in BuildCraft 2.2.0, originally named waterproof pipes, but as of BC4 they are called Fluid Pipes. Fluid pipes can be used to transport oil, fuel, water and lava to different locations. These pipes allow liquids to be transported into engines, tanks and oil refineries. When a pipe is not connected to anything, it will fill itself up instead of pouring the contents on the floor. Pipe Waterproof is crafted by placing cactus green into the middle space on a crafting bench. This is used to create Fluid Pipes. Fluid pipes, depending on material can transport more or less fluid than other fluid pipes. This is represented as "mb/t" in game, which stands for millibucket per tick. 1000 mb = 1 bucket.
All pipes except for obsidian pipe and Lazulli Pipe can be turned into a fluid pipes by placing pipe waterproof on top of a wooden pipe, cobblestone pipe, stone pipe, iron pipe or gold pipe. Fluid pipes will only connect to other Fluidpipes. They will not connect to transport pipes or Kinesis (conductive) pipes
Wooden Fluid Pipe (10 mb/t)
Wooden Fluid Pipes allow any buildcraft compatible liquids to be extracted from a buildcraft compatible liquid storage container and into an adjoining buildcraft compatible pipe network. This is done by placing a running buildcraft compatible engine next to the wooden fluid pipe.
Also allows you to connect Cobblestone Fluid Pipes to Stone Fluid Pipes and vice versa.
Wooden pipes can interconnect different type of pipes, but cannot connect to further wooden pipes; a normal cobblestone or gold fluid pipe must be used instead.
Note that it is unnecessary to use a wooden fluid pipe to extract liquids from pumps.
Cobblestone Fluid Pipe (10 mb/t)
Cobblestone Fluid pipe is a basic fluid pipe. It has a regular capacity for liquids, and it can transfer buildcraft compatible liquids along a network of fluid pipes.
This pipe will not connect to any stone fluid pipes, similar to stone and cobblestone transport pipes not connecting.
Stone Fluid Pipe (10 mb/t)
Stone Fluid pipe is a basic fluid pipe. It has a regular capacity for liquids, and it can transfer buildcraft compatible liquids along a network of fluid pipes.
This pipe will not connect to any cobblestone fluid pipes, similar to stone and cobblestone transport pipes not connecting.
Iron Fluid Pipe (40 mb/t)
The iron fluid pipe has up to five inputs and one output.
It will send all incoming liquids in one direction. The direction can be changed by right-clicking the pipe with a Wrench in 2.0.x. The output direction can also be changed by redstone current. Every time it either loses or gains redstone power, it will cycle to a different output. However, it will never output to a Wooden Fluid Pipe. This combination of properties allows for players to accurately control its output direction from afar, via redstone wiring. In addition, this can be used to distribute liquids among multiple pipes by using a redstone clock. Players who have not mined enough redstone can simply use a Wrench.
Gold Fluid Pipe (40 mb/t)
Gold fluid pipes will transport more liquid than stone or cobblestone waterproof pipes. They do not need a redstone current to operate, although a powered wooden waterproof pipe is still needed to extract liquids from tanks and some machines (e.g. not the pump).
Emerald Fluid Pipe (40 mb/t)
First available in BC 3.4.2 (for MC 1.4.7)
Emerald fluid pipes will drain 4 times more liquid at once than wooden fluid pipes.
Sandstone Fluid Pipe (10 mb/t)
First available in BC 3.2.0 (for MC 1.3.2)
Sandstone fluid pipes connect to other kinds of transport pipes, allowing stone and cobblestone fluid pipes to connect, but will not connect to machines or any other blocks, allowing more compact piping around machines.
Void Fluid Pipe (10 mb/t) *'BuildCraft Transport' Mod
As of this writing, it is unknown when first available.
Void fluid pipes dispose of fluid.