There are many threads in this forum about this problem.
Personally and on advice from friends here, I used a wet kit. It comes with liquid especially made for our sensors and dry swabs.
Here's a link to the many threads on this subject.
PentaxForums.com - Search Results
And here is the one where I was told to use a wet solution to get rid of the offensive stuck dust. This one is pretty long in the tooth because I had problems with the first kit, and second, I have shaky hands.
https://www.pentaxforums.com/forums/pentax-beginners-corner-q/101908-how-sensitive-sensor.html