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I don't have a sink in my LG, but I do in the SideKick standie. I've used it for brushing my teeth, and that's about all. It's too much of a hassle, to me, to hook up the drain hose under the travel trailer, along with the collapsible 5 gal jug to collect the gray water, and then to find a "proper" disposal place.
I bought a collapsible dish sink from Camping World ("smashes" down to about 1" tall), but I have yet to use it. This is perfect for me, especially since I don't really want to wash dishes in the rear of the LG. I have a table that I use for cooking and washing--keeps the rear of the LG cleaner and free of accidental spills.
My water heater, when I have shore power, looks like a coffee pot, but doesn't have the coffee making "guts". It provides plenty of steaming hot water to wash dishes. And, it heats quick enough that I don't run out of hot water. If you find you need a lot of hot water when you're camping, try to find a 32 cup coffee maker with a spigot. They're marvelous for heating water for whatever you need. They can be found used at Goodwill stores, or at stores in your area that have used kitchen "stuff".
If I don't have shore power, I just put a sauce pan on the propane stove to heat water.