Q. Does one have to wash with soap before Shabbos begins?
Is someone just stays under the shower for tisha kabim, is that enough lechatchila?
I think it is about 2 minutes, is that correct?
A. Ben Ish Chai (Lech Lecha 15) explains that the soap stands in place of the “sicha” or rubbing in oil that was common in earlier times. Shulchan Aruch (O.H. 260: 1) includes scrubbing one’s head, Biur Halacha (ibid.) adds to use “nesser,” which is similar to soap. Piskei Teshuvos (260, n. 3) quotes a list of prominent Gedolim that did not use soap.
Poskim stress the importance of immersing on Erev Shabbos in a mikva (Chaye Adam in Zichru Toras Moshe 1: 2, Sheloh, Sidur Yavetz, Yesod Veshoresh Hoavoda 8: 1, Birkei Yosef 260: 3, see Mishna Berura 551: 95)
On question 590 in regards to taking a shower to comply with tisha kabim, during the nine days and Erev Shabbos, we wrote: “Many Poskim maintain that you comply with the custom of nine kabim (as an alternative to Tevilas Ezra, (see Mishna Berura 88: 4) by showering until that amount of water cascades on you. (Minchas Yitzchok 4: 21, Yaskil Avdi 7: p. 387, Taharas Yom Tov 19, Chelkas Yakov 3: 61, Minchas Oviv p. 202 et. al. However, Mishne Halochos 3: 1-7 and others disagree)”
Horav Shlomo Miller Shlit’a pointed out that one Kab is equal to the volume of 24 eggs and tisha kabim is then 216 eggs.
According to the measurements of Rav Chaim Noeh, one egg is equivalent to 57.6 cc, so nine kabim would equal to 12.44 liters (Shiurei Torah p. 263). Following the opinion of the Chazon Ish, it equals 21.6 liters (Midos Veshiurei Torah p. 300).
You have to measure your own shower’s water volume delivery as they all vary.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a