This has given me an AWESOME idea, thank you dave!
Here it is: Vine sap may be transported from machine to machine, by two methods:
1) The machines can share between each other, just by contact or:
2)HOLLOW VINES!
Hollow vines are a specially bred type of vine, and tehy can transport vine juice, and only vine juice, although far better than any other liquid pipe. This leads on to another idea:
1) Put the hollow vines in a crafting table. This will yield four vine walls.
2) Put 6 vine walls, along with a special grafting tool, and some string, in a crafting table(shapeless recipe). This will yield a vine tank block. This tank block can be placed in world, and any TBs connected to it will further enlarge the tank capacity, in a similar way to an LESU storage unit from GregTech.
The Hollow Vines will work faster if placed in direct sunlight, and the tank will gradually add 1 millibucket of sap every minute, when placed in direct sunlight, for every block there is in the tank (this may be too OP, I'll leave that to your judgement, whether to change or get rid of it, it is your mod after all
).
EDIT: This will be better or more useful in certain situations because of its sheer expansion power, and the fact that it can be any shape.