I had a well that wouldn't drain so I was investigating the problem, in the process I couldn't believe just how nasty my livewells had gotten. I use a SureLife product and Hydrogen Peroxide when the weather (Heat) calls for it like many others do. Obviosly it had created a thick mildewy type coating all over both tanks, come to find out it's very UN healthy for the fish being held in there, sometimes for extended periods..
You can power wash them like I did, or go to the car wash and hose them down good. Mine look like new again I also blew the drain hole out to find a 4" swimbait clogging the drain line laying on the ground, I guess one of my fish had spit it up and I never saw it before opening the drain...
Just an FYI, on helping keep our fish and livewells in good shape..

Lol was it one of your baits?

The toilet augger they sell at Home Depot with the spring on the end works well too. They make one that is PVC safe and small in diameter.

LOL.. Actually no, it wasn't.. I've had perch or shad in there before from other fish, but never an artificial bait that big...

Everything I've read on the net about how to clean a live well says that clorine is ok, and that it evaporates.
I actually tried it on a minnow bucket we keep here at the house and it cleans and gets rid of the smell.
There's some good videos out there..

Chlorine only evaporates from the sun, it'll hang around and stick if it doesn't see the light, I wouldn't put chlorine in my livewells that hardly see sun and it getting in drains and stuff it'll eventually break down and go away but takes awhile