Attempting to move Hydraulic Fluid from a Mixer (HC) to any tank using a Sluice (MariC) works.
Attempting to move the Hydraulic Fluid into the world :

• when more than a bucket of Hydraulic Fluid has been made doesn't do anything (can place a bucket of said liquid in world from hand)
• When < 1 Bucket of Hydraulic Fluid crashs with the following crash report: http://pastebin.com/qbX0Ae2p

However it doesn't appear to mind if it removes enough liquid to have < 1 Bucket left, only if there is < 1 Bucket when placing the Sluice.

Using version 2.4 of HC, 1.7.2 Beta 2 of Mariculture

Suggested fix, based on viewing similar code (not personally tested this):
In TileSluice.java, Line 116, check tank.drain(orientation.getOpposite(), drain, false) for Null first, then get the amount.

Fixed in 1.7.2 B3.