Ok, so once you’ve determined you should drain a pleural effusion, your options are to insert a small catheter (CVC, pigtail, generally 8.5 to 14F) or a traditional chest tube. CVCs/pigtails should only be inserted when (a) you have ultrasound guidance and (b) the effusion appears to be free flowing and without a great deal of echogenic contents. Why? Because to go in with a sharp needle, as the seldinger technique requires, you need to visualize a safe spot by ultrasound, and because if the effusion is complex with septations and blood/pus, it likely needs a large bore chest tube to successfully drain. For the less experienced, a traditional chest tube insertion is done using blunt dissection and exploration with a finger, such that the risk of pneumothorax is minimal (no needle).
In terms of the pigtail insertion, choose a spot using ultrasound, generally posterior to the midaxillary line to optimize drainage, then freeze, insert the guide needle then guidewire, then dilator and finally the drainage catheter.
Here is a makeshift video showing a pigtail insertion. I will make another one more focused on the technique, as this one is a bit more focused on the ultrasound. We ca see a large effusion with a bit of atelectatic lung, and also confirm the placement of the guidewire and the pigtail catheter.
Although in this video I showed live ultrasound guidance, in most cases I prefer to pick the spot, mark the skin, and do the technique blind. It is simply faster that way. However in some cases, especially with small fluid collections, I may choose to use live ultrasound guidance.
This is actually a very practical skill to have, as otherwise pigtails are generally inserted by interventional radiology, which implies delays, and more importantly, patient transport and its inherent risks and disadvantages. So for those without experience, I would highly encourage you to seek out an experienced operator and learn this technique.
Disclaimer: this description and video is for the sole intent of sharing medical knowledge and does not replace formal training. Do not try this without adequate training and/or supervision.