string TestRequest="<soap:Envelope xmlns:S=\"http://www.w3.org/2001/12/soap-envelope\" xmlns:ns=\"urn://x-artefacts-smev-gov-ru/services/message-exchange/types/1.2\"><soap:Body></soap:Body></soap:Envelope>";

_transport.PostXMLData(
"http://xx.xxx.xxx.xxx:7500/ws", 
"http://xx.xxx.xxx.xxx:7500/ws?SendRequest", 
TestRequest);

public string PostXMLData(string destinationUrl,string action, string requestXml)
        {
            try
            {
                HttpWebRequest request = (HttpWebRequest)WebRequest.Create(destinationUrl);
                byte[] bytes;
                bytes = System.Text.Encoding.ASCII.GetBytes(requestXml);

                request.Credentials = CredentialCache.DefaultCredentials;
                request.Headers.Add("SOAPAction", action); 
				
                request.ContentType = "text/xml; charset=utf-8";    
                request.Method = "POST";

                
                request.ContentLength = bytes.Length;

                Stream requestStream = request.GetRequestStream();
                requestStream.Write(bytes, 0, bytes.Length);
                requestStream.Close();
                HttpWebResponse response;
                response = (HttpWebResponse)request.GetResponse();
                if (response.StatusCode == HttpStatusCode.OK)
                {
                    Stream responseStream = response.GetResponseStream();
                    string responseStr = new StreamReader(responseStream).ReadToEnd();
                    return responseStr;
                }
            }
            catch (Exception exp)
            {
                _log.ErrorLog(exp.Message);
            }
            return null;
        }