Having had yet another botched transition from a kerb to the road (and possibly some underinflation) I’ve heard that horrifying thump as the weight of the steel rims and the lock crashed down. Sure enough, I woke up to a flat. Thinking it is just the pinch from the kerb and nothing else, how are my chances of fixing it just by pouring some DocBlue in? It’s a hub, so changing the tube is something I’d ratger avoid for now if I can
Latex based sealants are great at fixing the sort of small holes that you'll get from thorns and glass. If the hole is too big, then all of the sealant will just rush out with the air in your tube. Pinch flats tend to make a big enough gash in the tube that sealant is useless.
People will often talk about using sealant to avoid pinch flats because they're talking about an entirely tubeless system. This means that the sealant replaces the tube altogether, leaving nothing to pinch at all. Unfortunately this can't just be done on any setup with any old tyre, making it an expensive venture if your wheels and tyres aren't already tubeless ready.
Once you've fixed the flat, the best solution (without spending $$$) to avoid pinch flats is just to run higher pressure in your tubes.