I have a bird with it as well. How do you drain?
(Below is a cut&paste from one of my prior posts, there are also some articles and a few YouTube videos to guide you)
I have a little ritual of: bringing them inside, snack! (Super special snacks

) , bath to wash the bum, (and I get better visibility of the bum with wet feathers) , then disinfection of the whole area (Bactine is locally available so that is what I use).
The location of the hole is better understood with the videos online, but generally speaking: right side of the bum hole, down about 2 inches, across about the same (2 inches left, 2 inches down, that is a diagonal away from the bum, because you don't want to puncture the colon)
I puncture with an 18 gauge needle (I no longer use the plunger part of the syringe. I found using the plunger was uncomfortable to them, led to a lot of painful squirming and sad cooing sounds).
The needle goes in around a quarter inch ( 0.25"), which is around a centimeter if that makes more sense to you. You really only want to make a break in the outer skin for the liquid to drain, it isn't in an organ.
Once punctured you wiggle the needle a little and the liquid will find the escape route.
Then allow her to drain either through the needle or by removing the needle and letting the hole drain. The choice is not mine, some drain better with the needle inserted some don't need it.
If she doesn't need the needle in place she walks around and it pours out of her comfortably. ( This is a mess on the kitchen floor but seems easier on her to drain if she is moving around)
If she needs the needle I keep her still and massage the abdomen to direct the liquid out. I worry about her moving around with a needle in her so I limit movement.
After I disinfect the whole area of the hole. (Sometimes this means another bath If the liquid got the feathers dirty)
I can't say they enjoy it, but they have a nice active life afterwards, so I'll keep at it.
I keep them in the house away from the others until about a day after the liquid has stopped. Sometimes longer if they seem to be sleeping a lot and are poorly.
I have noticed that some of them had reduced their eating due to the liquid pushing their organs so they need a lot more calories when they are drained. Some of them spend a few days in the house eating constantly. I know you think "all chickens eat constantly" but really constantly, I know chickens love food, but this is just impressive.
I give them chick food or other high protein chicken food. I try yogourt -not all of them love it. Some of them will only eat fruit flavoured yogourt

(spoiled? Yeah...)