With Forestry and OpenComputers installed fluids can be duped with a robot. I tested this without forestry installed and robots cannot use buckets like tanks. This seems to be with something with how forestry handles its buckets.

With the following versions, a person can use an OC robot with a tank_upgrade and a tank_controller upgrade to infinitely dupe any bucketable fluid. All you have to do is have the robot run the following script and it will dupe the fluid

while true do
component.tank_controller.drain()
robot.drop()
robot.suck()
end

It will continuously drop the bucket and then pick it up and reuse it.
I will be opening a ticket with OpenComputers as well so they can assist from their side.

Minecraft: 1.12.2
Forge: 14.23.4.2705
OpenComputers: 1.7.2.67
Forestry: 5.8.1.322

Sorry, wrong repo