The Carpenter can only process liquids that are stored in its tank. To this end, you have two solutions:
- Simply pipe the liquid from your squeezer to the carpenter.
- Place the cans in the top-right-most slot (that is marked with a water drop).
As with water, seed oil should be able to be pumped into the carpenter from any side.
Also, make sure you are running the latest version of Forestry. The ability to use seed oil in the carpenter is a very new feature.
As a sidenote, you don't need an alveary to use bees. Apiaries are more than sufficient for starting out. Ignore this, I didn't notice the updated recipes in the latest version.