Crash Log - https://gist.github.com/anonymous/e3b8d4ed272ec8bb6ea2#file-gistfile1-txt-L70

BC tank containing water

Using Extra Utils node to pipe water in and Mek pipe to remove it (using tank as a buffer)

Have you managed to reproduce the problem without using any other mods?

In addition:

Do not open an issue if you're not planning to fix it, instead open a thread on http://mod-buildcraft.com/forums/index.php?board=2.0

Always include the version you are having trouble with. Or if you're building from source, which source you're building. If you don't, we might assume that you are using latest-greatest and waste a bunch of time trying to reproduce a problem that might have fixed been already. Such things makes for very grumpy devs. Grumpy devs spend less time coding and more time doing stuff that makes them less grumpy.