Can you identify this film?

Alba's pick sure looks good. Wiki link is missing the closing parenthesis, here it is again.

before getting that tab sorted, i searched for "movie man kidnapped bathtub" and got

https://upload.wikimedia.org/wikipedia/en/6/6f/Where_the_heart_is_poster.jpg

hmmm, close!

"movie man kidnapped bathtub acid" gets us closer to the right genre/vibe but no obvious hits. it seems like there was a real life 1940s serial killer, John Haigh, the "Acid Bath Murderer," who inspired a fair number of fictionalized accounts. ex. an episode of the radio program The Black Museum called "The Jar of Acid." apparently Hitchcock kicked around a version called Kaleidoscope.

oh, thanks alba, i may yet start thinking of you again as 'king of research' 8)

and i'm glad it turned out to be quite obscure!

yeah, there's an 'acid-bath' keyword in imdb but doesn't turn this up. in fact, imdb doesn't mention acid bath part of this at all.

there's an "a is for acid film" from 2002 that's about Haigh that i remember watching at the time. that one does turn up in the imdb keyword search (but is far too new)

Dante's Peak, while not exactly bathtub-based, is my go-to for such "acid cinema"

i may yet start thinking of you again as 'king of research' 8)

I've still got it! FWIW, this took just one Google search; was probably a bit of a fluke though. The clever thing is that all Wikipedia pages about films contain the word imdb. Can't remember if I was thinking that carefully when I constructed the search. It was the 10th result for me, so only just on the first page.

doesn't make the front page for me

duckduckgo (which i've been using recently because image search is easier) has it 3rd though.