Glen, no one quite explained what occurs in these "dry sump" engines, so I will take the time to explain so you understand. Due to the ring package and cylinders that not necessary have good support/structure (poor engineering) these engines tend to take on quite a bit of crankcase pressures. Those pressures are from not only combustion (exhaust stroke) gets past the ring package, but it's also from air/fuel as well during the compression stroke (piston ascending after intake valve closed) that gets past the ring package as well. Lets just call this a design flaw. The second design flaw is in the scavenge section of the oil pump. This is the component (gear) that is suppose to draw oil from the crankcase and put it back through the filter and into the dry sump tank (oil tank). Not only is it not that efficient in doing it's job at idle, it's pretty poor at doing it's job under rpm. If you where to build this engine out of lexan whereas you can see what's going on, you would see that at idle, it barely functions (the scavenge stage) and it's poor at best in getting that oil back to the tank. Ok, now image if you over fill it by double the amount of oil it should actually have. You've just taken that little area in the crankcase away that holds anything that comes past the ring package, and displaced that area it with oil. Where does it go? Well, it is forced up the cylinders through the oil return area and starts filling up the tapet cover area and before you know it, it belches it out of that vent tube which is hooked to your elbow that goes into your carb, and even though you are not seeing oil it pouring all over the place, it is getting consumed back into the engine. This is why it pours white smoke out. You might ask as to why someone would ever design a system whereas the breather tube goes right back into the engine. It's required by the manufacture to have the engine re-consume any sort of crankcase pressures.
Now, if some knucklehead at S&S would have designed the scavenge stage correctly for that light weight and half useless ring package, then this would never be an issue, and in actuality the engines crankcase would have vacuum and not pressures.
I know all about these systems and how they work, as I have been doing this for 33 years. Our scavenge side to the oil pumps for the engines we build in my shop, have 23 to 25 inches of vacuum in the crankcase while the engine consumes over 450 pounds per hour of fuel. That's the engines air and fuel consumed to make 175 hp per cylinder. Multiply that by 2 and you have two cylinders that are actually the same bore and stroke as these S&S engines which only make about 105. The math of the same bore and stroke in our engines would make 350hp per the 2 cylinders.
P.S. On my own personal Big Dog, I vent through the one way valve and run that line down the front frame tube and it is cut open under the bikes frame. I am only interested in burning 2 parts, and not 3. (Air and Fuel) Not air, fuel and oil.
