repair technician to do the job for free, the results would be disastrous if your own efforts went wrong. If the connection failed while tightening, or worse, the pipe actually broke, you’d have 50 litres of water or more spewing into your basement each minute, with no way to shut it off. Perhaps, if you’re quick on your feet, you could grab some vise grips and flatten the end of the pipe to slow the flow until the main valve could be shut off at the street, but that’s not a DIY experience I’d wish on anyone.