Lucas has managed to scratch open a cyst on his back. Have bathed it for some time with boiled water with a little salt added and gently squeezed out (I think) all of the fatty contents along with I hope the sac. It has bled quiet a bit but is now dry and I've put some sudocrem on. I shall obviously keep and eye on it but is there any else I should have done or do? Many thanks.

My Shola used to have one on her back which would just burst. I used to wash it with salt water and put Savlon cream and wound powder on it.

How did you ensure that all of the sac came away?

I use surgical spirit, alternatively Whitch hazel

I bathe anything like this with epsom salts , then sprinkle with lanacane powder.

I boil water, let it cool off, and use a very dilute solution of Hibiscrub.  Usually use Sudacrem after, as my own vet said it was totally safe to use.

I think you have done the right thing.
If it hasnt dried up and gone down in a week, I would take your dog to the vet for further treatment.
Salt, whether its plain or epsom, is very good for this type of thing.

Im not sure I would bother with any creams of any type, but you seem to know what you are doing!
Watch for signs of the cyst filling up again or redness around the site.

Sounds horrid...how did  he get a cyst...?