I see its a good time of year to do a water drain of the diesel filter (because of the potential for any water in the filter to freeze).

I know how to drain the filter, undo drain screw on top of the filter and it drains out of the bottom, but I have a couple of questions:

1) Will only water drain out, i.e. if there is no water in there will nothing come out or will neat diesel drain out.
2) Dependent on the above if I drain into a glass jar, will it be obvious if there is water in there.
3) Will it need priming after? 
Hung like Einstein, smart as a horse.

1. Drain until neat diesel comes out.
2. Yes
3. No

2/ the water if any will be obvious the diesel floats on top.

And it will be colourless.

Cheers, I thought the diesel was colourless (you guys aren't using red are you? ) 
Hung like Einstein, smart as a horse.

It's a pale yellow colour, a bit like

Knew I should have fitted a drain tube when I last replaced the filter. I had to disconnect the filter and remove it to drain it, otherwise it meant draining it into the engine bay with no idea what was coming out. No water drained out anyway, it was a yellow blueish colour immediately. Fitted a drain tube to it this time before putting it back. 
Hung like Einstein, smart as a horse.