I have a device that looks like a *very* large bottling wand with a gravity valve at the bottom. A thin hydrometer fits inside, and you push it down into the carboy, suck on the end if you need to draw the beer further up, bring it out, take a reading and let the beer drain back down into the carboy. It works pretty well though you have to sometimes take a couple readings to average out the effect of any bubbles in the liquid. They're widely available in BC but I don't know if they are anywhere else. I believe they are made in France.