ציטירנדיקער פּירוש אויף שמות 40:31

ורחצו, an imperative, seeing that the letter ר has the vowel patach. If this had been a form of the future constructed with the introductory letter ו, the letter ר should have the vowel kametz under it. Examples are: Exodus 40,31 ורחצו ממנו. Avraham meant to tell his guests to allow themselves to have their feet washed by one of his servants.

For K'riat Shema and prayers - And one may recite the blessing "Al Netilat Yadayim" - for we learn [in the Talmud], regarding the wash basin [in the Temple], [the verse states] "And they shall wash from it" (Exodus 40:31), but not from within it (ie. dipping hands into it); but in general (ie. not regarding the Kohanim in the Temple), even [dipping] within it [is permitted]. But to remove the evil spirit, it requires specifically pouring 3 times, and dipping [one's hands] into a vessel, even 100 times, is only considered [like they were dipped] once, for immediately [after the first time] the water became impure and is considered to be like [water that was already] poured. For this reason, [the Shulchan Aruch] was in doubt afterwards regarding [dipping into] 3 separate waters, because it's possible that you don't specifically need pouring 3 times in order to remove the evil spirit, maybe just washing them is enough; or perhaps you need to specifically pour water from a utensil onto your hands. The Pri Megadim wrote that based on this, if one dipped their hands in the river 3 times, or in snow that's on the ground in 3 separate places, even then it would only work for prayers, and one could recite the blessing "Al Netilat Yadayim". But there's a doubt whether it would suffice to remove the evil spirit, because maybe it requires pouring [water] from a utensil. Artzot Hachaim and Levushei S'rad ruled that [dipping hands in] a river, or in snow, or in mikveh (ritual bath) water is sufficient to remove the evil spirit, even if they do not have 40 sa'ah. See further in Artzot Hachaim.