I have been looking for information and cannot find a clear example of an s-trap. I guess that the difference between the two is that a p-trap has a horizontal trap arm directly after the trap and an s-trap goes directly into a vertical pipe. I assume the problem is with velocity of the water being drained. In case of the kitchen sink, with the trap directly under the sink as normal and then a 2 and a half foot drop before a vent pipe joins would cause the water to reach such a velocity in that vertical 2 and a half feet, that siphoning would occur.In the washing machine, with a 4 foot drop down to a vented p-trap under floor, again the initial 4 foot drop would allow the water to reach such a velocity that the trap would be subject to siphoning. Is this the problem (regardless of whether the vertical drop is before or after the vent)? If it is, could I install a 90 degree elbow to slow down the vertical drop of the water? (FYI: I am building my own house myself in a country that does not have vented plumbing - one reason for building my own house. Therefore I cannot have a pro. install the system and I have no one with the know-how to ask questions. Also: both washer and kitchen sink are under windows which the vent pipe must circumvent. Due to length of horizontal run, I would need a 2" vent pipe in these exterior 2x4 walls. These quadruple studs beside the windows are also where my seismic anchors attach and I would seriously compromise the integrity of these walls by notching or opening a hole in the studs.) Would a loop vent for an island sink application work? Thanks for valuable information.