gistfile1.cs

        void RefreshProxyQueue()
        {
            var proxyQueue = queueFactory.Create();
            var query = from provider in proxyProviders.ToObservable()
                        from proxy in provider.GetActualProxyList()
                        from isAvailable in IsAvailable(proxy)
                        where isAvailable
                        select proxy;

            query.Subscribe(proxyQueue.Enqueue);
            queue = proxyQueue;
        }

        IObservable<bool> IsAvailable(ProxyInfo proxy)
        {
            return Observable.Start(() =>
            {
                bool result = proxy.IsAvailable();
                //Log...
                return result;
            });
        }