Philly Marathon Hydration Vest

Hi all!

I will be running the philly marathon on sunday and I wanted to check with any of you the rules for the hydration vests. I use the CamelBak Women's Circuit Run Vest 50oz Hydration Bladder which includes the space in the back for the hydration bladder. I’m understanding from the philly marathon website that hydration vests are allowed in as long as the bladder is empty, but does anyone have the experience to confirm this? I just dont know if this might be seen as a backpack or something and not be allowed in since they are discouraged.

Thank you all in advance! :D

https://www.philadelphiamarathon.com/info/faq/