Clove oil works, but I've never used it myself, so I'm not really sure of the dosage or anything. I'd imagine you could find that pretty easily though.
Why do you need to knock out your fish? Clove Oil is suppose to work and can be found at any Pharmacist (sp? sorry its early). Sometimes sold as Eugenol or a as a remedy for toothache
Clove oil works, but concentration of the the active ingredient (eugenol) can differ a lot between brands/batches etc.. an OD will kill your fish without a problem. If you can't get hold of a commercial anaesthetic (aquiesce, benzocaine etc..) it's best to test the oil that you buy on feeders first @ about 40mg/L (approx 2ml/5L...don't know what this is in ounce/gal) (This is for salmonids) if this has no effect after 3-4 mins, up the dose incrementally (waiting a few mins each time) until reactions slow down/loss of equilibrium. If fish start to roll on side you're as far as you want to go (if they roll all the way over it's pretty much curtains). This'll give you an idea of the conc'n that you need. If you are then using it on a big fish remember that gill SA/Body volume ratio is smaller so don't be surprised if you need a little more to take effect.
I would recommend that you don't anaesthetise unless completely necessary and if you do make sure that you try to get hold of a commercial fish anaesthetic (try a vet) first.