One of my semi quick cleaning tasks recently was to degrease the vents on the underside of our microwave. When I cleaned the microwave I made a mental note to come back to those. And one morning I remembered!!
They simply slide out. I dropped them in the sink with some Dawn dish detergent and warm water to soak. I did end up leaving them too long. I know this because the water got cold and grease was still attached. I repeated the process, but made sure to scrub with a nylon brush while the water was warm and soapy.
They didn't come out perfect, but they are better! I remember having a really greasy vent at one home. It took many, many soaks to get it better. It was worth it though at the time. Now, if I were to come across a really greasy vent, I think I would try to find replacement ones. I did a quick search on Amazon to find that the pair I have above would cost $9.95 to replace.
Have you ever replaced your grease vents? Do you clean yours?