Hello,
I am planning to build my home with an island kitchen sink and I am trying to prevent sudsing issues.

My desire to keep the plumbing within the joist depth, has led me to an air admittance valve instead of island vent loop.  The air admittance valve is 40″ above the direction change, which is 20″ short of being 40 pipe diameters.

While designing this house, it made me realize why my current apartments sink plumbing with similar set up slows tremendously when using  sudsy soap… am I wrong  in thinking that is the problem… suds backing up into the trap and above it?

any thoughts on how to improve my design?