First thing I'd try is one rounded edge plus circle spline in a sweep-creator. The inner angle is the crucial part here. If this doesn't work out well - weld 2 cylinders (8 iterations) in a 90*angle via Boolean add. Get rid of the crease and ploys you don't need, optimise to weld points - then edge loop select the edges at 45* and try your luck with Polygon->chamfer (or alike, I'm not in front of my Mac right now). I'd extend/double/mirror/rotate the parts till I got bigger elements to double, stack and align&swell with snapping and optimising.
Does it needs this fittings to mimic real pipe-work or could it be just a bent hose?