Q. This year we ended the Sedorim very late, almost at 5.00 AM. To keep awake can one drink coffee after eating the Afikomen.
Can one use mouthwash after eating the Afikomen?
Kovetz Halochos p. 458 maintains that although one can drink tea after eating the Afikomen, one should avoid coffee since the flavor is stronger.

Horav Shlomo Miller’s Shlit’a opinion is to permit coffee as needed. The Rov also permits the use of mouthwash since one does not swallow it.

Rabbi A. Bartfeld as revised by Horav Dovid Pam, Horav Aharon Miller and Horav Chanoch Ehrentreu Shlit’a