The first drysuit I ever owned had nothing for bladder relief...and I swore I'd never have another one without it. My new one just has a zipper in the lower front, and I find that's fine for the diving I do...I don't do any tech diving, just SCUBA and air, so I can easily go the length of a dive between "pees". But, I do a lot of multiple-dive days, and peeling off a dry suit between every dive to relieve myself got very old very fast. So, the zipper works fine.
One thing I have noticed is that it's much easier to hold the bladder in a dry suit than in a wetsuit...not sure why, maybe the cold water down the back and over the kidneys. I know many divers just let fly in the wetsuit when they need to...but I can't bring myself to do it...I know, I know, but I just can't. So, I took an old drysuit pee zipper and installed it in my wetsuit. If I feel the need to go while in the water, I open the zipper and turn my back to my buddy. Very quick, and I feel much more comfortable for the rest of the dive.
I've never used a p-valve...can someone explain exactly how they work? It might be an option for my next drysuit, and I'm due for one soon. The word "catheter" doesn't thrill me, though!