When you say "probe" are you talking about the "Pan Evac" system or is it some measuring probe?

A Pan-Evac doesn't have a "probe" but what it does have is a 1/2-inch metal pipe, the same as you can buy at a hardware store. The weld-in pipe is threaded on one end (to attach the exhaust check valve) and the other end is cut at a 45-degree angle. It is this cut end that is positioned in the collector such that the exhaust stream passes over this cut end drawing air from the crankcase into the exhaust stream.

It works much like an old fashioned perfume vaporizer, air passing over the end of a tube draws perfume into the airstream.

As for required positioning of the pipe, from testing and experimentation the optimum placement is in the collector. If you weld the pipe in farther downstream, the effectiveness is reduced.

If it is some other "probe" you are speaking of, please excuse my explanation.