According to Ruth Delany [Ruth Delany and Ian Bath Ireland’s Royal Canal 1789–2009 The Lilliput Press, Dublin 2010], the Royal Canal’s fast passenger-carrying fly-boats had neither toilets nor cooking facilities; the slower night-boats were better equipped.
So how did the fly-boat passengers relieve themselves?
Given that the boats travelled at six Irish miles per hour (about 12 km/h), any passenger who disembarked for the purpose would have found it difficult to catch up again. Yet standing on the notoriously unstable boats might have been difficult for the gentlemen, while the problems facing the ladies are not to be contemplated.
I don’t think that the india-rubber urinal had been invented by then. So what did they do?
Irish waterways history 