I am bored with the cold so I am trying to start a cutting in a simple SIP (made from 2 liter bottle). Just to make sure I understand. The goal is never to add water from the top- right? Only add water to the bottom so theoretically no gnats-right?

See this explanation: http://www.selfwateringplantershq.com/how-does-it-work/

I mainly use SIP's (Sub Irrigated Planter )for rooting now. The success rate is phenomenal.

If you cover your cutting with a plastic cup, you effectively create your own green house that will trap the moisture.

Just keep your eye on the amount of water in the reservoir. That's all you have to do.

The biggest danger that you will encounter is when you re-pot as you could sent the plant into shock especially if you re-pot too soon or disturb the roots.

For valuable cuttings, I like to use larger SIP's than a 2 liter bottle, so that I don't have to re-pot and disturb the roots for at least one season.

Thanks for the link

Gene, that is correct.  You start with moist potting media but never add water to the top.  It is probably best to not add any water (or very little) to the bottom either until you see roots.  Then add enough to saturate the wick of the 2L bottle SIP.