A configuration of a blood microtubular filter/dializer used in many kinds of renal replacement therapy systems can provide highly a effective mechanism for removing air from the blood circuit of such systems. In embodiments, for example, the invention takes advantage of the slow flow rate that usually occurs where blood exits the microtubules into a header area of the filter to provide a settling area and an auxiliary port with a multi-way valve allowing gas to be drawn out from the header and for medicaments to be injected into said header.