When I played teachest bass (more than 30 years ago) I used an old bow string I had left over from my archery days. It was one I'd made myself (for a 55lb recurve, using dacron) so the loops at the ends were properly served and all I had to do to attach it at the bottom end was use a wooden toggle inside the teachest and make sure it didn't chafe against the teachest's soundboard. It sounded fine but I couldn't be bothered with the hassle of trying to fit it into the Corolla so I gave it away and took up lagerphone (initially) and then concertina. My brother converted a teachest into a very upmarket-looking bass and used a string from a double bass; it sounded fine too.

Although I'd heard of washtub basses (as equivalents to teachest basses in style and context) they were mostly described by (and as associated with) North Americans; I've not seen any in Oz.

Cheers, Rowan