That is, as effluent is admitted to the vessel the rate at which liquid is withdrawn from the vessel is determined by the rate at which a liquid constituent of {TAIL ~ the effluent} enters the vessel so as to maintain {HEAD ~ the preselected level} of liquid, or liquid bed 
That is , as effluent is admitted to the vessel the rate at which liquid is withdrawn from the vessel is determined by the rate at which a liquid constituent of { TAIL ~ the effluent } enters the vessel so as to maintain { HEAD ~ the preselected level } of liquid , or liquid bed
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH