How to filter elements connected between two mechanical equipment informed by the user?

I'm having difficulty making a filter for a system consisting of pipes, accessories, pipe connections and mechanical equipment. This filter returns all elements in the view. But I just want the connected elements mentioned in the title.

FilteredElementCollector FEC_EM = new FilteredElementCollector(doc, doc.ActiveView.Id);
FEC_EM.OfClass(typeof(FamilyInstance));
FEC_EM.OfCategory(BuiltInCategory.OST_MechanicalEquipment);
foreach (FamilyInstance FI_EM in FEC_EM)
{
    Parameter EM1 = FI_EM.get_Parameter(BuiltInParameter.ALL_MODEL_INSTANCE_COMMENTS);
    TaskDialog.Show("EM1", "EM1: " + EM1.AsString());

    BoundingBoxXYZ bb = FI_EM.get_BoundingBox(doc.ActiveView);
    Outline outline = new Outline(bb.Min, bb.Max);
    BoundingBoxIntersectsFilter bbfilter = new BoundingBoxIntersectsFilter(outline);

    BuiltInCategory[] bics = new BuiltInCategory[] {
    BuiltInCategory.OST_PipeCurves,
    BuiltInCategory.OST_PipeFitting,
    BuiltInCategory.OST_PipeAccessory,
    };
    IList<ElementFilter> a = new List<ElementFilter>(bics.Count());
    foreach (BuiltInCategory bic in bics)
    {
        a.Add(new ElementCategoryFilter(bic));
    }
    LogicalOrFilter categoryFilter = new LogicalOrFilter(a);
    LogicalAndFilter familyInstanceFilter = new LogicalAndFilter(categoryFilter,
        new ElementClassFilter(typeof(FamilyInstance)));
    IList<ElementFilter> b = new List<ElementFilter>(6);
    b.Add(new ElementClassFilter(typeof(CableTray)));
    b.Add(new ElementClassFilter(typeof(Conduit)));
    b.Add(new ElementClassFilter(typeof(Duct)));
    b.Add(new ElementClassFilter(typeof(Pipe)));
    b.Add(familyInstanceFilter);
    LogicalOrFilter classFilter = new LogicalOrFilter(b);

    FilteredElementCollector collector = new FilteredElementCollector(doc);
    collector.WherePasses(classFilter);
    ICollection<ElementId> idsExclude = new List<ElementId>();
    idsExclude.Add(doc.ActiveView.Id); 
    collector.Excluding(idsExclude).WherePasses(bbfilter);

    int nCount = 0;
    string report = string.Empty;
    foreach (Element e in collector)
    {
        string name = e.Name;
        report += "\n\nName = " + name + " Element Id: " + e.Id.ToString();
        nCount++;
    }
    TaskDialog.Show("Caixa delimitadora + visualização + filtro de exclusão", "\nEncontrado " + nCount.ToString()
        + " elementos cuja caixa delimitadora cruza" + report.ToString());
}