Hi Ole; congratulations on your new Sherpa! Needless to say, we're looking forward to photos of your wonderful new bicycle!
I'm a new Sherpa owner as well, and your query sent me scurrying to check mine. No, there is no BB drain hole, nor are there any vent holes in the stays or fork blades left over from construction as far as I can see.
This last has me a bit baffled; as a hobbyist framebuilder, I drill holes in those locations to allow hot air to escape while brazing. I haven't quite figured how Thorn was able to to avoid them, but figure they may have been filled afterwards, perhaps with solder or filler or -- even more clever -- the vents may be internal between the tubes. I shall have to see the next time I remove the seatpost to renew the grease there.
At any rate, I am delighted as it has saved me the trouble of plugging these holes myself. I often ride in desert regions where the talc-like alkali dust can get into every possible nook and cranny, so I have taken to plugging the holes with kneaded beeswax before such trips. I was touring the San Juan Islands in Washington State (USA) at the time of Mt. St. Helens' eruption in 1980, and returned home with my bicycle on the bumper rack of a car. I was horrified on my return to find the frame tubes were nearly full of talc-like volcanic ash, all of which entered through the frame and fork's vent holes. I had to do a complete tear-down and vacuum out the ash, even to the point of making little tube nozzles to seal at the vent holes in order to get it all out. Took hours. Worse yet, oils acted as a solvent for the acids contained in the ash, and things like my chain were rusted beyond recognition or use upon my return home after a six-hour drive. Campagnolo white lithium grease didn't do much to prevent corrosion, but everything lubed in Phil Wood grease came through untouched and factory-fresh after an overhaul. Boy, there are some stories I can tell from that trip!
The wheels, cranks, and drivetrain components of my new Sherpa are covered in a clear, lightly sticky coating that reminds me of cosmoline used as as a rust-preventive for shipping parts as far back as WWII. I used to see it still coating the engines on early Honda automobiles back in the days when I owned my repair shop. I presume Thorn used some sort of WaxOyl or Framesaver spray when prepping the frame and this may be the result of a bit of overspray. It certainly is tenacious, and resists even 99% isopropyl alcohol and some light detergents. Hopefully, there is some inside the tubes as well.
Assuming the frame has been treated internally to prevent rust, it seems really worthwhile for there to be no direct points for water entry. I know preventing water entry has long been a priority at Thorn, and I recall reading some of the earlier Nomads, at least, used stainless steel "blind bosses" for the water bottles that were closed against water entry. I suppose you could drill and tap the bottom bracket for a water drain, but with the newer external bearings, there should be little way for direct water entry provided you keep your seatpost well greased and use fenders. Parking the bicycle upright when left outside in the rain will do a lot to keep water from entering as well (+1 for leaning against a tree,wall, or fence or for using a kickstand or Click-Stand). Laying-down a bike in an overnight rain can do much to allow entry of water sideways through the bearings and vent holes, if present.
Best,
Dan.
