Ditto to the separation suggestion - the injured one needs to fully recover before you try putting her back in with the others (if you do). If you don't have another cage, you can use a 12 quart sterilite or rubbermaid container as a kind of hospital room until she/he's fully healed.
Keep her/him on paper towels until its fully healed. Feed well and supplement with calcium/minerals to help it heal.
Rinse the affected areas of the tail gently in warm water especially if you can see any bits of substrate or fecal matter sticking it. You can put the leo in a rubbermaid type container with half an inch of water if anything is dried on (for half an hour), to loosen it up first.
After it is clean, apply a dab of antibiotic ointment (it doesn't need to be thick). Generic is fine, you can buy a tube of triple antibiotic ointment at your local drugstore for around $5. Read the label; you'll probably apply twice a day until healed. This will be more effective than rubbing alcohol, stays on better, and doesn't sting.
Separate, keep warm, hides for security, paper towels for substrate, feed and supplement, and use ointment.
>>You could try dabbing some rubbing alchohol on the gash to keep it from getting infected and also what gecko_girl said seperate him from any other geckos until he heals
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Andrea A. 