symbology - Drawing selection custom selection box using ArcObjects?

I have some code that I'm using to selecting features in a certain extent. I already rigged the tool properly, so it selected the objects as needed, but I want to draw interactively the selection box the user is making.

I'm using IScreenDisplay.DrawRectangle method, but it pollutes the screen with many small rectangles. is There a way to clear up the old drawings in the screen?

This Draw method is being called from a mouse move event. Any ideas?

Here are two methods I'm using to do the dirty work:

    public override void OnMouseMove(int button, int shift, int x, int y)
    {
        if (button != 1)
            return;

        if (!_IsSelectOperation)
            return;

        endPoint = focusScreenDisplay.DisplayTransformation.ToMapPoint(x, y);

        envelope.PutCoords(startPoint.X, startPoint.Y, endPoint.X, endPoint.Y);
        DrawEnvelope(envelope, BuildSelectionSymbol(), focusScreenDisplay);
    }

    private void DrawEnvelope(IEnvelope envelope, ISymbol symbol, IScreenDisplay screenDisplay)
    {
        screenDisplay.StartDrawing(screenDisplay.WindowDC, 0);
        screenDisplay.SetSymbol(symbol);
        screenDisplay.DrawRectangle(envelope);
        screenDisplay.FinishDrawing();

    }

Here is the code for BuildSelectionSymbol

    private ISymbol BuildSelectionSymbol()
    {
        IColor fillColor = new RgbColorClass();
        fillColor.Transparency = 0;

        IRgbColor outlineColor = new RgbColorClass();
        outlineColor.Red = 0;

        outlineColor.Green = 0;
        outlineColor.Blue = 0;

        ISimpleLineSymbol lineSymbol = new SimpleLineSymbolClass();
        lineSymbol.Color = outlineColor as IColor;
        lineSymbol.Width = 1;
        lineSymbol.Style = esriSimpleLineStyle.esriSLSDash;

        ISimpleFillSymbol fillSymbol = new SimpleFillSymbolClass();
        fillSymbol.Color = fillColor;

        fillSymbol.Outline = lineSymbol;
        fillSymbol.Style = esriSimpleFillStyle.esriSFSHollow;

        ISymbol symbol = fillSymbol as ISymbol;
        symbol.ROP2 = esriRasterOpCode.esriROPNOP;

        return symbol;
    }

Answer

It stills draws all the rectangles, but I still need a way to clean them.

For the linesymbol, fillsymbol and symbol, set ROP2 = esriRasterOpCode.esriROPNotXOrPen.