You should take him to the vet immediately. There may be a slim chance that the vet can clean the wound and give your cat antibiotics to prevent an infection. I don't know where you live, but you could try the banfield clinics at Petsmart, those are not the greatest but they are inexpensive. I think you really need to find a good vet for this particular injury, just my opinion.
As the other poster said, the problem with a tail injury is that the tail is part of the cat's spinal cord and is vital to a cat's sense of balance. Accordingly, cats are EXTREMELY sensitive to anything on their tail, like a wound or bandage, because they feel it very acutely, and it upsets their whole "alignment". By the same token, a laceration or injury to the tail usually causes them to repeatedly lick the area.
If there is a chance the wound will heal and fur will grow back- and it sounds like there may be a chance! Then maybe the vet can put something on the tail, in addition to treating the injury, to keep your kitty from licking the area so it can heal.
In many, many cases tails have to be amputated because it is easier than a bandage or the mutilation that a cat does in reaction to treatment of the wound.
So- get your cat to the vet asap and that is the best chance you have for saving the tail! And as the others said, keep your kitty inside.
In this same vein, understand that male cats have territory, and your cats, being indoor/outdoor are at a disadvantage against the 100% outdoor cats who claim the outside territory. And rest assured they will find your kitties and fight them. Male cats roam a lot more than females. You should never let your male cats outside at night, ever, as you will just see more of these fights. Also your males should be fixed, which should help keep them from marking territory and getting into fights.
Just so you know, I am saying this as the mom to a feral male cat who lives 100% outdoors. My boy cat lost his tail, it had to be amputated, because of a fight he was in and the laceration did not heal. In the case of my boy kitty (william in the picture on my post :-)) his injury was in the middle of his tail. It never healed because he kept licking it. The amputation cost about $1000 overall. Save yourself all that money and just go to the vet and get him treated asap. And let people on this site know where you live, they may have some suggestions for inexpensive vet care in your area!! Good luck and please let us know how it goes, we all care!!