I requested a list of Tonks boat owners from the British Waterways Archive, and was sent one as taken from the Gauge Registers of the Birmingham Canal Navigations, the Grand Junction Canal, the Oxford Canal Company and the Warwick & Napton Canal Company, with in addition the Castleford gauge books from 1880 onwards and the Trent Navigation from 1800.
The list I received showed 17 entries of J. & S. Tonks, with 2 of J. Tonks, 2 of S. Tonks, 1 of Samuel Tonks, 4 of J. S. Tonks, 1 of S. & J. Tonks, and 1 of J. & T Tonks.Most of them are shown as having a residency in Oldbury and the dates covered are from December 1886 through to May 1930.
Unfortunately, our ancestor, William Tonks, who mastered the boat named "Eliza" and is shown in the 1881 census with many of his family, was not included.So perhaps he only mastered the boat and was not the actual owner!
No doubt you have obtained all the boatmen named Tonks from the 1881 census.