Implant tools and techniques for implantation of a medical lead, catheter or other implantable component are provided. The implant tools and techniques are particularly useful in implanting medical electrical leads in implant locations such as substernal spaces or subcutaneous locations. The implant tools include a sheath coupled to a sealing device. The sheath includes a continuous lumen that is in fluid communication with a passage of the sealing device. The lead is advanced through the passage and the lumen for placement of the distal end of the lead at the implant location.