Ninety-something percent of Burkey's pics involve placing a strong pinpoint light source a distance behind the subject shining towards the camera and using the subject to mask the light source. This works really well in subjects standing in phreatic tubes (cave passage cut by water under pressure, often circular ish cross section) and people ascending rope in vertical pots, because unlike shots only lit from behind the camera, by the photographer, it lights the tube in the background giving a full sense of depth/relief by lighting the background.
I'm wondering if this would be ideal in drains too? I mean take a boring reinforced concrete pipe, you might think it'd make a dull picture as it has no real features, but a photo of a subject standing centrally in an RCP with a bright pinpoint light on a tripod way down the drain masked out by the subject might make a brilliant pic really accentuating the circularness. I tried in mine levels to recreate that look but only on solo trips and remote camera and couldn't line it up right so gave up, but if there was a separate photographer and subject an RCP might be the perfect location for the technique, that Mark Burkey and Robbie Shone seem to have mastered in caves. They should get down a drain instead?
Sorry the_rubber_johhny for further digressing your thread. I promise I'll sober up, and shut up now.