I too, prefer J-Lube for its low cost, it's ability to be mixed however thick you want it, and its ability to coat both toys and tissues with an amazingly slippery and cushiony layer of lube.
However, in the back of my mind I know it says it's "For Veterinary Use Only" which implies a number of things. For one, it means the manufacturer hasn't gone through the expense of having it certified pharmaceutical grade by the FDA. Also, I assume it means avoiding the expense of using pharmaceutical grade ingredients and manufacturing procedures so this stuff could be contaminated with nearly anything, as long as the animal didn't keel over after a reasonable amount of time. After all, animals tend to have much shorter lives than humans, so who's to know if it causes polyps or cancer in 10-20 years? In addition, it's mostly used in veterinary assisted birthing situations, which is probably a lot less often than humans regularly using it for fun.
So, after using it for play, especially knowing it's still in there, possibly deep, I'm always a bit concerned. Washing it out with an enema is probably not a bad idea, but I'm not sure how effective that really is. I'm thinking of trying FuckLube since I hear good things about it.
Regarding a few other points...
For mixing a lot, fill a bowl with as much cold water as you want lube. Using a kitchen whisk, slowly add the powder while whisking to desired thickness.
For quick use with butt plugs, etc (not deep), just keep some handy in a parmesan cheese shaker. Add small amounts of powder and water to toy or hand until desired consistency.
For deeper play application, I've found that a Depezer catheter fits nicely on the end of a 60ml syringe. Just draw the lube up into the syringe and work the end of the catheter back and forth a bit inserting it as high as you want while slowly emptying the syringe. They tend to be around 15" long and it makes a very long and flexible fountain nozzle that applies lube evenly to the sides of the sigmoid. This works with any lube, also, not just J-Lube.