code: def drain_OD(q_plant, T, depth_end, SDR):
      
      nu = pc.viscosity_kinematic(T)
      K_minor = con.PIPE_ENTRANCE_K_MINOR + con.PIPE_EXIT_K_MINOR + con.EL90_K_MINOR
      drain_ID = pc.diam_pipe(q_plant, depth_end, depth_end, nu, mat.PVC_PIPE_ROUGH, K_minor)
      drain_ND = pipe.SDR_available_ND(drain_ID, SDR)
      return pipe.OD(drain_ND).magnitude
docs: Return the nominal diameter of the entrance tank drain pipe. Depth at the
      end of the flocculator is used for headloss and length calculation inputs in
      the diam_pipe calculation.
  
      Parameters
      ----------
      q_plant: float
          Plant flow rate
  
      T: float
          Design temperature
  
      depth_end: float
          The depth of water at the end of the flocculator
  
      SDR: float
          Standard dimension ratio
  
      Returns
      -------
      float
          ?
  
      Examples
      --------
      >>> from aguaclara.play import*
      ??