An Advent calendar shouldn’t be written as an Advent “colander,” but there have been several puns. “Each day the little Cratchits would peer through a different hole in the Advent Colander” was printed in The Times (London, UK) on December 20, 2001. A riddle has been cited in print since at least 2002:
 
Q: What do you drain your Christmas Brussels sprouts with?
A: An Advent colander!
 
An “Advent colander” has been printed on several images.
   
     
Wikipedia: Advent calendar
An Advent calendar is a special calendar used to count the days of Advent in anticipation of Christmas. Since the date of the First Sunday of Advent varies, falling between November 27 and December 3 inclusive, many Advent calendars, especially those that are resusable, often begin on December 1, although those that are produced for a specific year often include the last few days of November that are part of the liturgical season. The Advent calendar was first used by German Lutherans in the 19th and 20th centuries but is now ubiquitous among adherents of many Christian denominations.
   
Wikipedia: Colander
A colander (or cullender) is a bowl-shaped kitchen utensil with holes in it used for draining food such as pasta or rice. A colander is also used to rinse vegetables.
       
20 December 2001, The Times (London, UK), “Off the Leash” by Jack Malvern, pg. 18 illustration caption:
Each day the little Cratchits would peer through a different hole in the Advent Colander.
     
Google Books
The Crazy Christmas Joke Book
London, UK: Puffin Books
2004 (Originally published in 2002.—ed.)
Pg. ?:
What do you drain your Christmas Brussels sprouts with?
An advent colander!
 
Twitter
Regent Exeter‏
@RegentExeter
The Brussels Sprouts should be strained in an Advent Colander.
5:24 PM - 26 Oct 2009
 
Twitter
Boolbar‏
@Boolbar
I’ve just got an Advent Colander. Every day I can reveal a new hole.
5:37 AM - 16 Nov 2009
 
Twitter
HTFB‏
@htfb
It’s the first of December and I have a bowl of soaked split peas to drain and rinse. Time to get out the Advent Colander.
3:14 AM - 1 Dec 2009
 
Twitter
Paul Bell‏
@paulbellmusic
Every day this month I’m going to boil and drain a different vegetable. I’ve got myself an advent colander.
3:21 PM - 3 Dec 2009
 
Twitter
Katie Russell‏
@Sapphire2uk
What do you drain Christmas dinner brussel sprouts with?
An advent colander! !#itsacracker
3:36 AM - 12 Dec 2009
   
Google Books
Christmas Crackers
By Matt Wilce
Lulu Press (Lulu.com)
2012
Pg. ?:
What do you use to drain Brussels sprouts?
An advent colander!
 
Google Groups: alt.support.depression
Top 10 cracker jokes for Christmas 2012
.(JavaScript must be enabled to view this email address)
12/25/12
(...)
What do you drain your carrots with at Christmas? An advent colander
   
Google Groups: alt.humor.puns
Culinary Christmas
Nemo
7/13/14
Time to drain the 25th vegetable in the Advent Colander.
   
Google Books
Gigglers: Christmas Jokes
By Toby Reynolds
London, UK: Scholastic Fiction
2015
Pg. 38:
Q. What do you drain Brussels sprouts with?
A. An advent colander!
 
Twitter
Mr Sid‏
@bthooligan
@TedTerrier
What do you drain your carrots with at Christmas?
An Advent colander! 🥕🥕🥕🥕
3:30 AM - 8 Dec 2017