Double foam filters didn't work for me. Still had some oil misting on back of AC bracket and across front of oil tank to clean up after a ride. Ordered the discrete breather from DK and no more clean up (I've monitored the filter that attaches on the end of the hose and haven't seen any signs of oil yet).

 

I went for the vents routed up and to a catch canister, just recently switched from a filter to the canister. Seems to working fine when I switched to the canister there was no oil in the filter. So, the routing up seems ideal.

 

Correct, I don't like a filter when I can have a drain tube down at the swing arm

 

What you describe would, in fact, create a trap of sorts - as you say.

That said I question whether or not that is advisable for this type of application. here's my concern: a trap, such as you have in a sink is designed to always have water witting in it as a seal, to prevent sewer gasses from venting up through the sink drain and into the house. Unless the house is vacant for too long and the water evaporates the system is simple and reliable. It blocks or seals sewer gasses from passing through it because the water int he trap is denser (40x IIRC) than the air/gasses.

Now to our bikes: If a trap is formed and oil collects and resides in the lowest portion of the trap, my concern is that, just like the trap under a sink, it will prevent gasses from passing through it because the liquid oil is denser than the gasses trying to get through - creating a seal. Now, you may never know this because the volumetric capacity of hose between the engine and the trap would act as an expansion chamber of sorts and may be sufficient to vent the heads.

As for having or not having a filter, I will grant you that any airborne particulate in the atmosphere would have a hard time getting all the way up the hose and into your head(s), but, in an abundance of caution, I would sleep better knowing that my heads are not open to the atmosphere without some level of filter barrier.

I may be over analyzing things a bit and picking the fly poop out of the black pepper. Kinda like following the Owner's manual and staying below 3500 rpm when the bike is new.

 

I think the difference here is that compared to the water trap in the sink, the oil trap is pressured by the crank, so i would imagine that the force it has is enough to overcome any trapped oil enough to allow breathing. Might be wrong, but just comparing to the sink analogy. which the sewer gasses are just 'ambient' and have no force behind them.