securing the tubing to a hanger connection profile along a borehole of a tubing hanger;

securing a first check valve to first threads of a first landing profile along the borehole and above the hanger connection profile, the first threads including a first thread feature;

securing a second check valve to second threads of a second landing profile along the borehole and above the first landing profile, the second threads including a second thread feature, and the second landing profile being wider than the first landing profile; and

pumping a first fluid in a downhole direction through the second check valve and the first check valve into the tubing without permitting a second fluid within the tubing to flow in an uphole direction through the first check valve.