If it is the same material as the other walls, lower it's
Intersection Priority
so that it does not cut the walls that you are keeping. Though I believe that this will not fix all of your wall contour lines, but it will prevent there being a hole in your toilet wall, 2D fill and 3D.
If the
Building Material
of the removed wall is high than that of the retained, reduce the
Building Material Strength
of said
Building Material
, or turn off
auto-intersection
and do not intersect the reference lines of your removed wall with the retained. With these two, the
Building Material
change will have a similar result as the
Intersection Priority
change mentioned before while the
Auto-intersection
change will give you a thicker line cutting the joint between the two walls when you show existing.
Alternatively, and probably better, would be to put the removed wall on a separate layer and have that layer change
Intersection Group
between an existing and planned
Layer Combination
. This would be the best option as far as I know, but I do not work on renovations so there maybe a better way.
Ling.