Graeme. Hi
. Congrats on your 12". Don't worry too much about a little bit of dust. It accumulates all the time. Just take the nec. steps already stated & keep the ends covered in plastic when not used. Here's a guide to collimating.
http://skyandtelescope.com/printable...rticle_790.asp
In place of the 'Cheshire' (until you get 1), use a film canister. Put a 1~2 mm hole in the centre of the cap, assemble & place in the focuser. You may need to rotate it just to make sure the hole is in the centre of the cap............ Check in diff. locations as to how your collimation is going.
HTH.
L.