Can I use a 1/4" Stereo jack for the output of my pedal

[RjM]

Would I still use eh third lug for ground, or would I use the second lug, or can I even use a stereo jack?

[R.G.]

Yes, you can use a stereo jack for your effect output.

The proper terminology for the contacts on a 1/4" phone plug is tip, ring, and sleeve.

Tip is the contact at the very end. Ring is the ring just aft of the tip on a stereo plug. Sleeve is the barrel of the effect, the bit of metal that the conductors go through to the tip and ring contacts.

Sleeve is universally grounded.
Tip is universally signal.
Ring is not present on mono plugs, the sleeve being longer, going all the way to the tip.

A phone jack has spring contacts for tip and ring - if it's a stereo jack. If it's a mono jack, there is no ring contact, and no solder lug for it.

Using a stereo jack with a mono plug just means that the longer sleeve in a mono plug (like a guitar cord) will contact the ring spring contact, and ground it and anything connected to it. This is how the battery switching is done on many effects - the battery (-) is tied to the ring contact and is then connected to ground by the mono plug's sleeve.

To use a stereo jack where you are not trying to get it to switch power, just identify the ring spring contact and lug, and carefully do not attach anything to them.