var keepAlive = Task.Run(async () => {
  while(!cancelSource.Token.IsCancellationRequested)
  {
    Console.WriteLine("Checking alive");
    await Task.Delay(1000);
    if(cancelSource.Token.IsCancellationRequested)
      return;

    remoteStream.WriteByte(0xFF);
    await remoteStream.FlushAsync().ConfigureAwait(false);
    Console.WriteLine($"Flushing toilet. Connection is {_remoteClient.Connected}");
  }
}, cancelSource.Token);

//I get in console:
//Flushing toilet. Connection is True
//Checking alive
// even after turning the device off