W
Welder
Legally, I don't think it's not too late because the work was substandard but hidden on the day it was put in so you have a breach of contract claim (implied terms - standard of workmanship).
It's probably not worth the time or effort pursuing them just for this, however, do you really want to see how bad their second attempt is? For something this small, just get a proper plumber in or, if you have the requisite skills, do it yourself.
Whoever 'installed' that, certainly isn't going to give a flying kcuf about someone coming back to him about his 'quality' workmanship. Just get it sorted by a professional and learn from it.