Overriding the Default Activities" Tab"

This may be totally obvious, but how can I override the default activities tab? I get an error message if I try to create the VF page like so:

<apex:page standardController="<strong>Task</strong>" recordsetvar="c" extensions="skuid.Redirects"
action="{!redirect}?objectType=Task&amp;actionType=<strong>Tab</strong>">

And I can't see a place in Tasks Buttons, Actions, Links to set the override either.

Thanks!