Let try this:
ReportDocument oRpt = new ReportDocument();
oRpt.Load(Server.MapPath("CrystalReport.rpt");
oRpt.PrintOptions.PaperOrientation = [Shared].PaperOrientation.Portrait;
oRpt.PrintOptions.PaperSize = [Shared].PaperSize.PaperEnvelope10;
Then you use the code to printToPrinter