Cricket Question.

The black tube that the crickets use to lay the eggs, is that see able at all times of female crickets or does it only sometimes show?

From what I've seen with my crickets, the female's ovipositor (black tube) is always visible, although it can vary in size depending on the type of cricket you use and probably age as well.
If a cricket doesn't have one then it's most likely male. Male crickets just have two smallish spikes at the end of their abdomen.

Yes, it's always visible as long as the cricket is adult.
In younger females, the ovipositor can be seen less or more, depending on size as it develops its length together with the cricket.