It's a weird situation I know... and I completely agree! You would be doing me and the fish a huge favor by helping me with this filter-less hypothetical situation.
I am doing the fish a favor by telling you that it's a bad idea to get it without having filtration available.
I tried something similar before, and the lungfish died after I missed one of my daily water changes; in my case, the filter I had for it got messed up by snails, and I didn't have a backup, so I had to do large daily water changes instead.