Here's what I do (no special or homemade tool necessary).

Take a 3/8" crows foot wrench and put every extension you own on this thing, making a contraption that's about 3 feet long.

From the top, put the crows foot on the expanded part of the tube and smack the end of the extension with a hammer. Assuming the tube is started straight, you'll drive it straight in and bottom it out, while standing comfortably beside your car, no extra helping hands needed.

Jim