I've got a couple of water lettuce.... and am wondering how to disinfect them before placing them in the tank. Any input will be appreciated

Water lettuce is pretty, but I've never seen it for sale at petstores. Did you mail order it?

The most effective and gentlest way to disinfect plants is with pottasium permanganate crystals. You should be able to get some in the water department at a hardwear store, but I find its kind of hard to find now. You can also order some off ebay as always. You really don't need that much at all, 10 grams will be plenty. If you know any chemists I'm sure they have access to some....that's how I got mine