Okay, so I got buildcraft version 4.0.1 for minecraft 1.6.2 up and running two days ago, and I started messing around in creative mode.

The bug: I attach wooden pipes to the tanks to extract the liquids when powered by a gate or an engine, but when it is powered, the fluids will not be extracted! This is so annoying, I cannot extract fluids from tanks or refineries!

I can extract items from chests, and put fluids into tanks and refineries, but I cannot extract the fluids.

Cannot duplicate.

You are using fluid pipes right? Can you post a screenshot of your setup?

I believe I have solved the problem already, but thank you for your help.

Turns out it was an issue with the location of an autocratic gate on the pipe, not a bug in the programming. It was affecting the flow of the water into the main pipe system, so i deleted it, and sure enough, the water started flowing.

Wrong. I just tested again yesterday.

Oil and Fuel are not being extracted, but water and lava are perfectly fine.