How do I actually get rid of post nasal drip?

Pseudoephedrine
That exact med. Not the Sudafed with the useless phenylalanine nonsense that has been demonstrated to do fuck all. You may have to ask the pharmacist for it - it's not prescription but Feds made stores move it behind the counter. Ask for the generic, it's cheaper. Really works
Side effects suck though, dry mouth, maybe a little agitation. But it'll clear you right up.
- And it's a stimulant. Nothing worse than feeling miserable from a cold and unable to sleep because of pseudoephedrine.
  
  Try a lower dose, I can usually get by with half the recommended dose. Worst case scenario, add Benadryl to the mix to knock you out. Being able to breathe is worth it!
  
  This. I hate the stuff. Can't sleep and get a killer case of restless legs.
  I am prone to respiratory complaints, it's my weakness. However, I'd rather have that misery than pseudoephedrine.
- What they said plus Mucinex (or the generic) makes the goo more fluid so it can drain out faster/better. Irrigation with a neti pot or sinus rinse bottle can be a huge help too. Use 2 packets of the salt that comes with the bottle; the extra salt helps draw water out of the tissue to reduce swelling. Try to snarf the water down the back of your nose and spit it out of your mouth.
  Good luck. PND is annoying AF
  
  I think Mucinex has been demonstrated to be as effective as phenylephrine (i.e., not).
- Ask for the real Sudafed. The little red ones say 4-6 hours, but one lasts me all day and minimizes side effects. They work quickly enough that you don't need to get ahead of your symptoms, you can wait until you feel you need more.
- You make it sound like there was no reason to move it behind the counter 😂. Pseudoephedrine is a key ingredient in making meth
- So it turns out that phenylephrine spray (i.e. topically applied) is actually super effective. It only lasts for a couple hours, although it's insanely fast to start working.

Get allergy tests. Mine was allergies to pet hair, dust etc. I got a permanent fix unintentionally. Had throat cancer, the chemo and radiation damage drops the mucous creation to about 50%, so post nasal stopped being a problem. LOL
- Get cancer, got it.
  
  Doctors recommend this one weird trick!
- Good job on beating cancer <3
  
  Meh, I had a great team of pros. They did the main cancer fighting. I just mostly laid in bed feeling tired or in the bathroom vomiting. :)
- Seconding this - mine turned out to be an intolerance to cows milk (specifically, the casein).
- I don't know if to be hlad for you, or not.
- Damn

Go to an ENT and determine what the problem is.

Sinus rinse and flonase (the light mist one) work best for me.

theres a trick involving pulling on your ear and hard stroking your cheekbone.
theres another trick where you pull out nosehairs.
theres another where you eat spicy food.
some people use a neti pot.
- Don't pull out nosehairs. That's a great way to get a staph infection.
- If you are like me, the neti pot isn't nearly as effective as forced water with the bottle or a sinugator

Phenylephrine AS Ephrine Nose Drops.
It's ineffective orally, but it sure as heck works up your nose. Just occasionally though, you can get dependent, making things worse in the long run.

My dad used antihistamines

Flonase worked really well for me, bit it can be very drying for some people

Perhap remove the irritant? Maybe it's the air quality, bedding, or fabric softener?

A lot of water, dusting, washing your bed sheets, exercise, and watching your diet, all help a bit.
I like to take a hot shower, cup the hot water, and blow my nose into my hands until it stops being congested.
I also uh...picked my nose clean during this time, but I don't recommend this.