Walter's last name is Tabachnik, as can be seen on the name badge he wears in the scene where he's setting up the universal remote he gives the Suarezes as a gift. Yet, it's never spoken out loud nor is it listed in the credits.
Original not the 4th episode it's actually the 5th episode. SWAG Episode 11 is the actual main 4th episode on the dvds - online it's put back to Episode 11.