Regarding the water being Nolad, see מנחת שלמה חלק ב' סי' ל"ד אות כ"ט where he says it is clear that the water is nolad.
Regarding the plastic pipe, it would seem to be a question only according to the first opinion in סי' ש"ט סעיף ד about a bosis that will be removed on Shabbos [by a goy or a child]. The first opinion says it is a bosis, so your question would be, where it is being removed automatically does that change. According to the second opinion that it is not a bosis even if it won't go off by itself, your case when it empties itself would definitely not be a bosis.
The Mishneh Berurah (319/21) relies on the second opinion in the case of a loss.
Also, see עטרת שלמה קובץ זכרון תשס"ה pg. פז-פט where Rav Shlomo Zalman Grossman the Rov of Elad address this question.
Assuming that a 45 degree is not considered "on" an item, your point that "maybe only something ON something else can cause bossis", is like the ב"ח סי' ש"ח (סעיף ט"ז) ד"ה חלוק. However, the (פרי מגדים (סי' ש"ח משבצות זהב ס"ק י"ד says that even if the supporting item is above the Muktza it has the rules of a Bosis.