I first heard about the notion of cooking salmon in the dishwasher in nutrition school. The class was about finding ways to get our clients to cook more often at home, and since most people's No. 1 excuse not to cook is lack of time, the teacher offered this cooking method as one possible solution. You're going to do the dishes anyway, so why not cook dinner at the same time?
As you can probably imagine, I first found the idea intriguing and even comical, but as it turns out, it actually works. The salmon gets slowly poached, resulting in a perfectly cooked texture. If you wrap it well, no water (or soap!) will get into it, nor will the salmon's juices escape the foil and leave your dishwasher smelling of fish. I double wrap it in heavy duty foil just to make sure, but if you're an expert wrapper you may be OK with less.
Something you should keep in mind: onion and garlic don't cook fully in the dishwasher. I add them to the fish for flavor before sticking in the dishwasher, and then unwrap and slightly sauté them in some oil and pour them over the salmon before serving. You can also change the seasoning in any way you want.