We have a 2019 Jayco 264BHW and our trailer came equipped from the factory with a breather tube attached to the filler cap and connects to the top of the FW tank.
As a side note, I just replaced the standard filler cap with a locking filler cap. I've heard of a few stories of trailer water being contaminated by ne're do wells. I may be paranoid, but better safe than sorry.
2019 Jay Flight 264BHW, Rocky Mountain Ed.
2020 Ford F150 XLT SuperCrew, 3.5L EcoBoost w/Turbo