I thought it was a tuba, and it sounds like one, but looking around for pictures it seems the tuba is a smaller instrument. Is this an unusual type of tuba, or what?
Looks like a Sousaphone to me. :)
That is a Sousaphone, but this one is made mostly of fiberglass plastic (except for the small brass pipes and valves.) Other Sousaphones are made with brass parts (sometimes silver plated.) It is not "Home-Made" - Sousaphones are manufactured by several music instrument companies in the US, Europe and Asia. Sousaphones are usually pitched in BBb (old ones were also available in EEb) but Tubas are made in BBb, CC, EEb and F. (Euphoniums are usually Bb - just slightly smaller than the F Tuba, and Tenor Horns are Eb.)
i think the man in the photo is a member of "Los luthiers" (a group from argentina). if he indeed is, i bet he built his instrument quite probably based on a tuba. It is not uncommon for them to build their own instruments, with cans, bottles, etc.
Looks like a Tuba/Sousaphone. The smaller Tuba you're referring to is probably a Tenor Tuba/Euphonium.