"ku sil" in Finnish
In the Finnish TV Series Lovemilla, Episode 1 there's a phrase:

Toi on mun poikaystävä, Saku. Se on ihan kiva. Yleensä. Ja Sakun idioottikaveri Ämpäri. Kaikki sanoo sitä Ämpäriks, ku sil on aina viikonloppuaamusin pää ämpärissä.

What is "ku sil on aina"? And is there some idiom with "head in the bucket"?

I understand that there's some word game around boy's name, but I'm not sure about details.

Here is the video, btw: https://www.youtube.com/watch?v=Rjxt97zfF8o

Question

"ku sil" in Finnish
In the Finnish TV Series Lovemilla, Episode 1 there's a phrase:

Toi on mun poikaystävä, Saku. Se on ihan kiva. Yleensä. Ja Sakun idioottikaveri Ämpäri. Kaikki sanoo sitä Ämpäriks, ku sil on aina viikonloppuaamusin pää ämpärissä.

What is "ku sil on aina"? And is there some idiom with "head in the bucket"?

I understand that there's some word game around boy's name, but I'm not sure about details.

Here is the video, btw: https://www.youtube.com/watch?v=Rjxt97zfF8o

Answer

"Ku sil on aina" is a more colloquial way of saying "kun sillä on aina" which again is an informal way of saying "koska hänellä on aina". "Sillä" refers to this Ämpäri fellow.

I believe that the expression "pää ämpärissä" just implies that Ämpäri gets so drunk that he has to throw up, thus having his head in a bucket. I haven't seen the show so I can't be sure but that's the first thing that came to mind. I don't think there's an idiom involving the phrase.