Poke a hole in the bottom of a plastic cup and VOILA! Little dripper. To get really fancy I made my own with a cup and some IV line tubing when I couldn't put the cup where I wanted it to drip. Works well and it was free!
You can get Little Drippers for $6 online, if you like to have the valve and don't want to make one yourself. Petsmart is extremely overpriced on basically all there products, especially reptile. Their prices are the highest I've seen for most items.
I got a big one and little one thrown into the deal when I bought two of my chams. Didn't really need them but wasn't going to say no to free stuff. So I stuck the spigot from one into the other so now it has duel output valves on opposite sides! Works well for my two cages next to each other. I can water them both at the same time. I'm not the biggest fan of the little valves though...they're kind of sticky and get clogged easily on mine. But it works well enough for what I need it for. My other cages still have homemade drippers and they work just as well for just as long.
You can use just an aquarium airline valve on a tub like that (you can probably buy a bag with a few for a dollar at your aquarium shop). So probably is the little drippers. You can seal around the valve with a little aquarium silicone.
My DIY drippers are much more reliable then the ones with the spigots. I took a washed tall deli cup and filled it with water. I then cut a piece of old towel, 1 inch wide, double the length of the cup plus a couple of inches so the piece of toweling could lay in the bottom of the cup, go up over the top of the deli cup and down the side to the bottom of the cup on the outside. Try it first by letting it drip into your sink. You get a nice steady dripping, not too much, not too little. VOILA. It doesn't stop dripping until the water is gone.
All my cages now have these DIY drippers and I love them. So do my chams. BTH, you can use any container, I started with 1/2 gallon milk jugs and just cut the tops off. Just make sure your piece of toweling is long enough.