I do both only because I have a water valve on the toilet that is really hard to get all the water out with air. And the valve is cheap plastic and a pain to replace and $40.00. So I blow it out with air and put in pink stuff. I dial down air compressor to 35-40 psi.
But most people do one or the other IMO
2003 Majestic 23P... Northwest travel machine
2013 Arctic Fox 25W... Wife "doll house" for longer snowbird trips
2001 "The Mighty Dodge"... tow vehicle for "doll house"