I have experimented with xanthan gum mixed with water and it makes a thick, gooey liquid. I've read that guar gum is similar but the end result is more viscous. (thicker and gloppier) The most interesting thing I read was that combining equal parts of xanthan and guar gums will result in an even thicker substance without using a lot of the product, much thicker than either one on it's own.

I am asking if anyone here has much experience with either one? Any tips or tricks in using these to make a gooey slime would be appreciated.

Here's my one tip: When mixing in water, try to use a high-speed blender with a sharp impellor to ensure that it mixes well and has no lumps. Mixing any other way is frustrating, as lumps will form and never dissolve.