Most supermarkets have glycerin, in the skin care isle. Also look in Cake decorating. In Walmart I think it's also skin care, but also check by laxatives. Ask the pharm people. The cake decorating has been removed by most Wal-marts, but it would be there if yours still has one. The type I use is Humco USP.
I haven't gotten many of the flavors right yet! It's been weeks. But truth to tell I started with grape..too much grape! My lips were purple and my atty smelled forever. I liked grape NeHi soda, and this is what it tastes like(without the bubbles), but I cannnot stress this enough..add a drop and test *before* you add more! Marshmallow tastes great and you can't overdo it. It's good with chocolate and also with peanut butter. Marshmellow smooths out lots of too strong flavors.
I used 2 drops of banana cream in my banana liquid because it was weak..boy that perked it up!
I had no luck with the heavy dark flavors. But the fruits were much easier to make. I don't think the colors clog the atty if used sparingly. At least Walrus says it doesn't hurt his atty's and his customers aren't complaining.
have fun in your lab LOL