tank connections are welded to copper boiler. this connection is very soft compared to screw in threaded mounts which are usually a harder metal structure. copper boilers are sanitary but soft. Welded fixturecare easily bent and cracked. only braising will properly restore it. I'm using an adjustable 10" wrench to hold the boiler fitting. a 17mm wrench on nut. By holding bothe wrench handles. Squeezing handles together for a counter-clockwise rotation. I remove nut without twisting left or right which would stress the tank's fitting.