Yes you can use Drano in your drains even when you have a septic tank.
I have a septic tank and I use Drano to clear clogs in sinks, bathtubs etc and the Drano works just great and has done no harm to the Septic Tank.
However Drano while it's safe to use in your Septic Tank the Drano does actually kill off some of the good bacteria in the septic tank.
So you do not want to use too much Drano or use Drano too often when you have a septic tank.
But using just a little bit of Drano every once in awhile is okay when you have a septic system.
You should also use a plunger, plumbers snake etc to try and clear clogs mostly but Drano is okay when you need to use it.