Rotate element (pipe fitting)

Revit
1

Hello , i tried a little script to rotate pipe fittings around their reference axis , so i took fitting’s connectors positions as base , created an axis from the reference point in the same direction as the connectors’s line .
My problem is when i rotate many times, after one or two rotations, the connectors switch ( connector 1 position come connector 2 position and vice et versa) , and the direction of the line become in the opposite direction (so that change the sense of rotation) .
Can i find a second point (like the reference point) so that the direction of the rotation’s axis stay always the same , or maybe an other idea ?

2 
import clr

clr.AddReference('RevitServices')
import RevitServices
from RevitServices.Persistence import DocumentManager
from RevitServices.Transactions import TransactionManager


clr.AddReference("RevitNodes")
import Revit
clr.ImportExtensions(Revit.Elements)
clr.ImportExtensions(Revit.GeometryConversion)

clr.AddReference("RevitAPI")
import Autodesk
from Autodesk.Revit.DB import *
doc = DocumentManager.Instance.CurrentDBDocument

clr.AddReference("System")
from System.Collections.Generic import *

elements = UnwrapElement(IN[0])
angle = IN[1]
p=[]
for e in elements :
	#getting position of connectors
	points=[]
	try :
		connectors=e.MEPModel.ConnectorManager.Connectors
	except :
		try:
			connectors = e.ConnectorManager.Connectors
		except :
			p.append(None)
	for conn in connectors:
		points.append(conn.Origin.ToPoint())
	#reference point of the fitting
	ref_location = e.Location.Point
	#create line between connecors
	ligne=Line.CreateBound(XYZ(points[0].X,points[0].Y,points[0].Z),XYZ(points[1].X,points[1].Y,points[1].Z))
	#direction of the line between connectors
	direction=ligne.Direction
	#creating a line from the reference point and parralel to the connectors line
	longueur=ligne.Direction.GetLength()
	rot_axis = Line.CreateBound(ref_location,ref_location+5*direction)	
	#rotating elements
	TransactionManager.Instance.EnsureInTransaction(doc)
	ElementTransformUtils.RotateElement(doc, e.Id , rot_axis , angle)
	TransactionManager.Instance.TransactionTaskDone()

OUT= 0