Walter is Yamaguchi, a member of a Japanese tour group led by Don Knotts of Andy Griffith Show fame. The Captain and Tennille are in an area where Hawaiian petroglyphs are found, explaining what they mean, and Knotts appears and tells them to get lost. His character is obnoxious, making comments that the tourists supposedly don't understand English. When Walter's character starts talking to the other tourists, Knotts screams at him, "Yamaguchi, can it!" He calls Walter over, and says, "Yamaguchi, I'm not talking for my own amusement ... can I call you 'Yama'? I've heard all of this stuff before, and frankly, I'm sick of it. So shape up or ship out!" (Seriously.) Knotts describes the petroglyphs in a very lame way. When he is finished, he tells the tourists to wait for their bus, but they all crowd into Knotts' car which is like a dune buggy and they drive off screen with Knotts at the steering wheel.
Shortly after this, the Captain and Tennille are explaining about hula dancing at another location, and Knotts and the tourists show up again. Knotts provides a very rude explanation of what a dancer is doing, and then says the tourists can take a brief break. He intends to go somewhere with the hula dancer, who is very cute, but the tourists all start harassing him for some unspecified reason, and in the confusion, Walter leaves with her, getting his revenge on Knotts!
This show features some really bad lip-synching and also stars Kenny Rogers and David Soul of Starsky and Hutch fame, who sings. The IMDb page of the show suggests that this special also features John Byner and Jamie Farr, but this is incorrect.
Walter's daughter told me that her father used to get residual checks for his appearance in this show, which were for four cents. He took one of these checks, framed it and put it on his wall.
A video of the show is on YouTube, Walter's appearance starts at 16:11.