Some engines (lawnmowers, generators etc) have a drain valve on the carb, but generally fitting one on a carb not designed for one is never more than a bodge. Had that on my Weslake, where the carb is at a steep downdraft. But because the carb isn't designed for modification, there's no 'meat' to do a proper job. Result was where someone had attempted a drain valve cracked and I had to replace the float bowl (wasn't cheap, as it required other changes as the original bowl was NLA). On a monobloc I guess you could drop the main jet cap each time, but really? Running the engine dry at journey's end has to be a whole lot easier (and less trouble). Running lean for a short while at low revs isn't going to cause problems. I do that with all my engines when they're not going to be used for a month or so - including two strokes (chainsaws, generators, brush cutters) which rely on fuel for lubrication.
