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

[ecjnfp]

Hello everyone, 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());
            }