Trying to grow Sweet Potato slips

Wifey is interested in growing sweet potatoes again.  Instead of planting them in the garden and letting them go nuts (as before), she wants to try some sort of potato tower she read about somewhere (maybe Pinterest?).  So we need sweet potato slips to start the plant-growing.

After checking the usual of my (Southern Exposure and Baker Creek) and finding the slips to be expensive ($10 for 6 slips seems pretty pricey), we decided to try to grow our own before succumbing to a purchase.

We went to the local farm market and bought a $5 basket of organic sweet potatoes (maybe 7 slim potatoes in the basket) to use as fodder.  A few tooth picks, some collected rain water, and a few jelly and/or peanut butter jars later and we have 4 potatoes sitting in a south-facing window working to grow some roots.

Once they grow roots, slips (aka the plant attempting to send out runners) should form shortly afterward.  Supposedly, you just remove the slips and put those in water until they grow their own roots.  Once they have roots, you plant the slips to grow new sweet potatoes.

It is supposedly a lengthy process, but I have time.  I'm certainly willing to take that time to save ourselves some money.