You can splice into either of the valve cover vent tubes or even splice both together and then into the catch can. You can also splice into the PCV tube. Do not splice the valve cover vent tubes AND PCV into the same catch can. You will injest a lot of oil that way and the catch can will fill very quickly. Or, run 2 catch cans, one for PCV and one for Valve covers. If you are getting oil in the filter, you may have excessive blow by from the rings or valve seals and a catch can will only give you minimal help. You may want to check you PCV and see if it is working properly. Clogged PCV can push crankcase air through the valve cover vents and into your filter and intake.
Good luck.
Mike
