I have a few 6ds and I am constantly changing lenses and because of that I tend to get dust on the sensor. I get it cleaned professionally. Can the C100 sensor be cleaned by yourself or do you have to send it in? How often does it need cleaning?

I clean the sensor from my dslr's before every shoot with a arctic butterfly, some might complain that it's expensive for what it is but I did not have to send a dslr in ever for cleaning since I started shooting with it a few years back. I might get dust inside while switching lenses but I check after I switch ed a lens and use the arcttic butterfly again if necessary.

This is the best way to clean your sensors (and lenses too)

How to Clean Your Camera and Lenses

I've literally never had a spec of dust show up on my c300, and I'm not exactly the cleanest guy when it comes to handling/storing my camera. There is an IR glass filter that sits in front of the ND filter mechanism that keeps dust out of the chamber, and besides those ND filters there are no other moving parts inside the camera like the mirror in your dslr, which makes the Cinema Eos cameras generally different animals than in this regard. I don't think you can clean the actual sensor on this camera yourself, but you can clean the IR filter.

But there's always gary's option

I have to admit to testing a GoPro in the toilet, but somehow I don't think I'll be dipping the C-100 in there any time soon. My attitude toward lens and sensor cleaning is basically not to do it unless it's really, really, REALLY necessary. I remember the question of cleaning the big mirrors of Astronomical telescopes came up in an Astronomy class and the response was to never do it - the cleaning would cause more damage than the bird poo.