To get to where you can post, use these clicks to take you to the form:
Click http://www.geocaching.com/hide/report.aspx
Click http://www.geocaching.com/seek/default.aspx
Click http://www.geocaching.com/hide/report.aspx
GoTo: Cache Type
Select from pull down menu: Cache In Trash Out Event
Below is discussion on what those links are and what you see when you click them.
To get to where I could post my CITO event, I used this link http://www.geocaching.com/hide/report.aspx from the official homepage for Geocaching - The Official Global GPS Cache Hunt Site (http://www.geocaching.com).
On the left, under the link titled "GETTING STARTED", the link below it, labeled "HIDE AND SEEK A CACHE"
Clicking on that second one takes you to http://www.geocaching.com/seek/default.aspx
This page is split in half with a heading on the left column saying "Seek a Cache..." in green
a heading on the right colum says "Find a Cache..." and is blue
This is one of those times where you are supposed to read the directions and learn about what you are getting ready to do before you are allowed to do it. Not a bad idea. That's what the first couple of paragraphs and links are for. But what you are looking for is the next link to take you to the "Online form", so click that to get to http://www.geocaching.com/hide/report.aspx
On the first open line is the "Cache Type". Use the pull down arrows to drop the menus down.
Select "Cache In Trash Out Event". The second line is for the "Cache Size". I selected "Other (See description)" and gave details about the size of the area to be covered and the amount of time set aside for the event in the details.