use a piece of 0.25inch nylon pipe, push one end into your merlin top port, the other end into your microbore. Close/seal off the inlet and product lines of your merlin and turn your pump on to full flow - leave it to run for about 15mins and it will do as good a job as any flushing kit if not better as you are using pure water, only problem is if your merlin has not been flushed in a long time then the membranes may be soiled and need a high pressure flush that you get from the flushing kit.