Tell the guy who built to pull them out and weld in the baffles properly, I wouldn't let him bail on a half assed job you paid to have done correctly. His problem if he has to build new tanks.
Wouldn't care if he lost money
on the job, his fault for not doing it right the first time.
I imagine this was an expensive job, go at him with a letter from a laywer right off the hop to show you're serious.
Next up would be small claims court, be a pretty simple one to win.