Steam Boiler Drain Clogged

Hello all, I have a Slantfin steam gas furnace and nothing is coming out of my drain valve. I tried to poke inside with a wire hanger and did see some gonk on the end wire but no luck. I'm thinking to remove the drain valve and start poking inside with the wire. I just want to confirm if this is the right approach. I have read when there's a lot of gunk in the tank water in the sight glass is muddy, but as you can see the water is clean (regardless, I still want to flush the tank). The other thing that concerns me is the water in the site glass is waaay above the recommended water line level. So i'm not turning this puppy on until I get that to correct levels and thank is flushed with clean water. Thanks in advance for you help! EP