disable web proxy for a WCF client?

In your Binding configuration, set useDefaultWebProxy=false

You can tell WCF not to use the default proxy by setting the BasicHttpBinding.UseDefaultWebProxy to false:

<client>
    <endpoint address="http://server/myservice"
              binding="basicHttpBinding"
              contract="IMyService" />
</client>
<bindings>
    <basicHttpBinding>
        <binding useDefaultWebProxy="false" />
    </basicHttpBinding>
</bindings>