To update on my own post.
Actual flight with the cath was a non event. I wish I'd had a window seat
I did get up to stretch and empty my bag a few times.
Outbound, went through WTMD, no issue. Return, went through the scanner. I told them before I went that I had a cath/bag. They sent me through anyway. The remote screener clearly saw the bag and guessed what it was as they asked me if I had one on the far side. The screening consisted of me touching my pants (on the outside) where my bag was, getting hands swiped, and then chemical sniffed. Except for about 5 minutes wait for this step, the process was painless. No pat down. Oh I had emptied the bag before going through least I be accused of carrying more than 3 oz of liquids
I'll be doing it again in a few weeks.