How to "clean" a geometry for meshing

Hi everybody,

I'm quite new with occt, i'm sorry if my question if quite obvious. I want to consolidate a list of solids (here 5 boxes) up to get a "clean" geometry to mesh.

I found an old post and i try this piece of code which work pretty fine :

TopTools_ListOfShape shapes;
shapes.Append(BRepPrimAPI_MakeBox(gp_Pnt(0, 0, 0), gp_Pnt(1, 20, 20)));
shapes.Append(BRepPrimAPI_MakeBox(gp_Pnt(1, 0, 0), gp_Pnt(3, 20, 20)));
shapes.Append(BRepPrimAPI_MakeBox(gp_Pnt(3, 0, 0), gp_Pnt(4, 20, 20)));
shapes.Append(BRepPrimAPI_MakeBox(gp_Pnt(0, 0, -3), gp_Pnt(20, 20, 0)));
shapes.Append(BRepPrimAPI_MakeBox(gp_Pnt(0, 0, -5), gp_Pnt(20, 20, -3)));

BRepAlgoAPI_BuilderAlgo builder;
builder.SetArguments(shapes);
builder.SetNonDestructive(true);
builder.Build();
TopoDS_Compound compound = TopoDS::Compound(builder.Shape());

STEPControl_Writer writerStep2;
writerStep2.Transfer(compound, STEPControl_AsIs);
writerStep.Write("file.stp");

But when i open the stp file with gmsh for instance, i get a lot of duplicated vertices/edges/faces. Is there an easy way to merge shared geometric objects ?

Thank you your help.

PS : Maybe using BRepAlgoAPI_BuilderAlg is not the best way to achieve a clean geometry.