what is draining my battery on my 1996 subaru outback
Sorry , but that is almost impossible to answer without actually looking at your vehicle . A good independent shop should be able to solve this . If you are the US most Autozone stores can test your battery and it just might be your problem .
After parked, engine off, any light remaining on? Look inside glove compartment, hood, trunk too. And look at tail lights, they’ll sometimes remain on b/c of faulty brake light switch. Beyond that, shops have methods to figure it out, but may take quite a bit of effort on their part – meaning a wallet-hit to you. A standard battery/alternator test makes sense as a start.
Assuming the battery is actually being drained then it’s either a bad battery or the parasitic current draw is too high.