It is fully compatible with buildcraft pipes and Liquid Loaders/Unloaders. It can only be manually filled from the top and when placing a filling pipe (for example, from a water pump), one has to ensure at least a 1-block gap between the filling pipe and the sides of the tank if the filling source isn't above the top edge of the tank. Placing a pipe next to the side of a water tank will connect it and allow water to drain out.
To build it, you will need 26 Water Tank Siding in a 3x3x3 hollow structure (no block in the middle). This is the same construction pattern as a Coke Oven, however, the water tank does not change its appearance once constructed (the Coke Oven, when built correctly, changes appearance and displays a window in the middle of each side). To check the tank has been built correctly, one has to right click it which will bring up the GUI (shown below). If the GUI does not appear then it has not been constructed correctly.
One can also fill the water tank manually by placing a water bucket into the top bucket slot. The bucket will empty and by moved to the bottom slot, with the water being added into the tank.
- Note: This plays an important part for the Railcraft steam locomotive, which is currently still in development.
Source: Railcraft Wiki