The Gemoro says “ Mayim Acharonim Chovah “(mandatory ).
Tosfos says " today we are not Noheg with Mayim Acharonim because we do not use Melach Sodomis" (Sodom Salt)—
In Shulchan Aruch (O Ch. 181) the Mechaber Paskens Mayim Acharonim Chovah.
There are some Kehilos who have the minhag of not washing Mayim Achronim.
The Leket Yosher* writes ," even though we don’t wash Mayim Acharonim during the year, but on Seder night we should wash Mayim Achronim for the love of the kosos (Chibas Hakosos)
We follow more chumros at the Seder".
In the Simanim** at the Seder we have twice for washing
(Urchatz & Rochtzo) Why don't we have a third Siman for washing Mayim Acharonim?
The Machzor Vitri quotes the Simanim of R.Yosef Tuv Alam.
Instead of 15 Simanim ,he has 28 and29*** . There are
3 Simanim for Netilas Yodayim,
1)Karpas 2)Motzie 3) Mayim Achronim.
*R. Yosef ben Moshe, compiled all the Halachos and Minhagim
he heard from his rebbi the Trumas Hadeshen.
** קדש ורחץ -נרצהנדש ורחץ etc.
***Motzei Shabbos adds “Havdalah”