Sirius and the Witch's Hump

[cindysphynx]

No: HPFGUIDX 36062

This is one of those questions that has probably been discussed 
before, but I can't remember the answer, so here it is again. :-)

In PoA, Sirius gains entry to the castle twice.  He does this (I've 
always thought) by entering Honeydukes and entering and exiting the 
castle through the witch's hump.

In Snape's Grudge, Harry sprints through the Honeydukes tunnel to 
get back to the castle quickly.  He "reached the inside of the 
witch's hump, tapped it with his wand, stuck his head through, and 
hoisted himself out; the hump closed . . ."

If a wand is required to open the witch's hump from the outside or 
the inside, then how is Sirius managing this?  Sirius clearly 
doesn't have a wand, as he spends the last chapters of the book 
using other people's wands.  If a wand is not required to open the 
witch's hump from the inside, then why does Harry do it when he is 
in such a hurry to get back to the castle?

Similarly, once Sirius is inside the castle, how does he get out if 
the witch's hump closes automatically?

So . . . how is Sirius getting into the castle?

Cindy