mine is the same way, it came with a long piece of filter material that you are supposed to cut and fit it in there. --WARNING stupid question--would i be able to not put the filter in and use it as a vacuum source?

 

i dont know for sure, but i dont think that would work out well for the sensor - is that even a vacuum source? i thought it was supposed to be atmospheric. i dont know, wouldn't do it.

 

just a thought