A high pressure evaporator vessel in the form of a flash tank (111) with a cylindrical body (113) is described. The upper end (117) has a vapour outlet and pipe (118) through which steam may be vented and the lower end (115) has a slurry inlet/outlet port (119). The slurry inlet/outlet port (119) comprises a fluid inlet conduit (121) which extends vertically upward from a restrictor (123) to a terminating end (125) above which a deflector assembly (127) is mounted. The inlet/outlet port (119) has an outlet port (129) which commences at a drain (131) which extends circumferentially around the fluid inlet conduit (121). The inlet/outlet port (119) includes a Y-piece (133) which directs fluid flowing from the drain (131) to an outlet (135) to which an outlet pipe (137) is connected. An annular insert (139) is press-fit in the Y-piece (133), and is shaped to cleanly divert flow from the drain (131) to the outlet (135). The inlet/outlet port (119) and associated fittings are also claimed.