app.config

Under "configuration" section in Web.config add this:

<system.net>
    <defaultProxy enabled="true" useDefaultCredentials="true"></defaultProxy>
</system.net>

If you need to consume from HTTPS location add this configuration:

<message clientCredentialType="Certificate" algorithmSuite="Default" />

WebProxy.cs

WebService wsrc = new WebService();
wsrc.Proxy = WebRequest.DefaultWebProxy;
wsrc.Proxy.Credentials = CredentialCache.DefaultNetworkCredentials;

WebProxy2.cs

WebService wsrc = new WebService();
wsrc.Proxy = WebRequest.DefaultWebProxy;
wsrc.Proxy.Credentials = new NetworkCredential("name", "******************", "domain");

WebProxy3.cs

WebService wsrc = new WebService();
wsrc.Proxy = WebRequest.GetSystemWebProxy();