Your looking for the General drop head auger from General spring and wire.
( Pennsylvania) They are available from any plumbing supply cost approx. $27 Pays for itself 1st time used. They come in various lengths.
The only problem is with the new 1.6 GPF this kind of head some times has a hard time passing through.
You dad is correct about this tool. I have made over $3000 from these money makers as I have them on all my vans. GREAT PRODUCT