The Poskim discuss the ideal way to set up an oil Menorah. Hacham Bension writes,as quoted in the Sefer Ner L'sion (8:29), that it is preferable to first prepare the wicks and then add the oil. This is the order found in the Ben Ish Hai’s “L’Shem Yihud” (preparatory prayer) for lighting Hanukah candles. Hacham Bension cites the work Galya Raza, who prescribes this for Shabbat candles. He also cites the Gemara in Masechet Yoma and the Rambam (Hilchot Temidim U’Musafim 3:12) which indicate that this was the way the Kohen would prepare the Menorah in the Bet Hamikdash. It follows that preparing the Hanukah Menorah should ideally be the same, but this is not mandatory.
The Kaf HaHaim (Rav Yaakob Haim Sofer, Baghdad-Israel, 1870-1939) (671:32), in the name of the Yafe LaLev, recommends adding water to the cups of the Menorah, so that the oil floats to the top. This alluded to the elevation of the Jewish people, likened to oil, over their enemies, akin to water.
Although using ready-made oil cups for a Menorah is permitted, one who does so is not able to fulfill these Hidurim-enhancements of the Misva. He also loses the opportunity to engage in Tirha D’Misva-toiling for the sake of the Misva by manually preparing the Menorah each night.
Ideally, one should manually prepare the oil Menorah, first inserting the wicks and then adding the oil. It is praiseworthy to add water to the oil.