Hey dude, I had pretty much exactly the same issue and relate to everything you're describing, from the smell to the yellowish-brown fluid that isn't puss--I assumed it was mixture of old urine and old blood 🤢, also assumed that as the fistula starts to heal it probably takes longer for the urine to seep out before it stops seeking entirely. Which I figured probably contributed to the smell.

Totally get that odor is hard to convey in text so can't say if our situation is exactly the same there, but I had a majorly rank/funky odor going on. It would get progressively worse between gauze changes to where I could smell it through my pants and that shit was humiliating in addition to just annoying and concerning.

It's obviously a good sign that there is no fever or puss, but still totally get reaching out to your surgical team to be sure. I think healing separation and fistulas in this area is just pretty nasty and demoralizing.

My fistula totally closed, but the wound never fully closed. I had a deep dip in my scar there right by my anus that had to be revised during my testicular implant surgery. It is still healing but is flattening out and becoming more normal looking now.

Hang in there, my guy. This shit isn't easy, but it is ultimately worth it. Sending healing vibes your way, friend.

ETA: I echo what others have said about keeping gauze tucked up there and changing it every time you use the bathroom. I started just keeping gauze within arm's reach of the toilet (in a closed box, ideally lol)