The people at Schwab are IDIOTS! Doesn't matter if they were in a hurry. I'm sure you were paying them to mount the tire/tube. If it takes another 5 or 10 minutes so what, do it right. The tube is comprised just squeezing into the slot. A valve extension won't do squat to prevent it rupturing and like Crane Op said the extension can crack easily. I'd go back and talk to the manager and tell him you want it done properly with a new tube. Anybody with half a brain would realize the tube is compromised and an extension won't protect it from failure. Sounds a little like the idiot putting tubes in my skid steer tires. Bead wasn't seating because he didn't use enough lube so put in over 90 PSI trying to seat the beads. I had to tell him to stop or he probably would have put 120 or more PSI in causing an explosion! This was a major tire shop too. A tire or tube explosion can be very dangerous.