When I first did this setup, the cam cover catch can would fill up with a very oily water mixture. It was mostly oil, with just enough water to make it a foamy, slow draining goop.

This was in contrast to the crankcase catch can's liquid catch, which was mostly just a slightly oily water. It would drain quickly.

That told me that I needed to stop the oil vapors in the cam cover, as in precipitate the oil from the blowby, before it got to the catch can.

The pic illustrates what I did. I used a copper scouring pad, known as a 'chore boy' here in the States, to be the precipitator inside the cam cover, under the vent elbow.

I secured the scouring pad in place using some SS wire to tie it down using s couple of holes drilled in that wall in the cam cover.

Once I installed the chore boy, the cam cover catch can no longer filled with mostly oil/some water. Now, that catch can just catches mostly water....just like the other catch can does.