I was cleaning my lenses when I suddenly realized... I had no idea how to clean the back element of the lens. I asked Google and he only talks about the front of the lens and how you can earn money by working at home. Kidding aside, I always cleaned the rear using a blower and lens pen but I have no idea if it's the right thing to do. With that in mind I ask; How do you properly clean the lens butt. Is it different from cleaning the front? Do you need specialized tools (butt cleaner, butt brush, butt blower, etc)? Does cleaning it using a pen or cloth damage the glass?
In addition (this is optional), kindly include ways to properly clean certain kinds of impurities commonly found on the rear element (smudges, dust, sand, slime, etc) and the tools you use.