Figuring out if a surfactant is present
There are multiple issues that need to be addressed before one can give a definite answer to this question. Let's start by what we are certain about:

1- The soap is not the issue (unless you haven't rinsed the barrel thoroughly with water). The remnant soap would be so dilute that should not cause any problem.

2- Since the film keeps forming there seems to be an equilibrium issue for your oil to separate. If you look into partition coefficients of the oils you should be able to estimate how much will remain in the water. Anyway, the less water you have, the more oil you can collect. (concentration factor pushes the oil out to keep the equilibrium) One idea is to add less water to your feed. 

3- THEORETICALLY one way to enhance oil extraction is to use a nonpolar solvent. HOWEVER, I STRONGLY ADVISE AGAINST ACTUALLY TRYING IT AT HOME due to the flammable nature of most nonpolar solvents and health issues related to it. If you can find a nonpolar benign solvent (that is a big IF), mix it with your final water oil mixture, and then decant the water from the bottom and then distill the solvent out to get the oil as a residue. 

4- Depending on the chemical structure of the oil, some of it will always remain in water. If they are not highly hydrophobic, it might be difficult to separate them from water anyway without using an assistant solvent.