Hey,
Last time I used a little jubilee clip on the nipple.
There's a difference between bleeding from dry and simply flushing through the old fluid with new fluid.
If your brakes are good and you just want to change the fluid then just use the bleeding method described below and you should be fine.
If you've let air in to the system or your brakes are otherwise not good then you'll need to bleed them properly. In my experience it's not so bad a job.
I've used one way values and mighty vac systems etc but for me nothing works so well as the old fashioned manual method followed by tying up the lever and leaving it over night.
I recently bled from dry after fitting new caliper's and brake lines, and found I was able to get the brakes 'okay, just about passable' within 10 minutes of manual bleeding.
But then after tying up the lever and leaving overnight you ought to wake up to find them spot on in the morning. (You'll never really bleed all the air out from dry by pushing it down, the brakes auto bleed as used).
I won't go in to tremendous detail on the bleed process as I'm sure you know it and there's loads of videos showing the process, but they key point is to proceed slowly and carefully so as to not mix up the steps and suck air in. Remembering that, it's just a matter of first popping your spanner on the bleed nipple and then a bit of tube over that, and then repeating these steps:
1) With the value still closed apply gentle pressure to brake
2) Whilst maintaining gentle pressure on the brake, open the bleed value. As you open the value the brake will give and fluid will be expelled.
3) Whilst maintaining gentle pressure on the brake, close the bleed value. Don't over-tighten.
4) Release the brake. Fresh fluid will be pulled from the reservoir.
Repeat as above, and take care not to let the reservoir run dry or you have to start over.
Don't stress about getting them perfect - get them okay, tie back the brake lever with a strong rubber band or tape or whatever then leave it over night.
It'll be better in the morning (technically it'll be better after the first couple of pumps of the lever in the morning).
If you look at the reservoir when you pump the brake (even with the bleed value closed) you'll see it expelling bubbles via the top of the system and pulling fresh fluid in.
Hope that helps, Andy