venting for gas water heater.

I have never posted any thing on the forum before. I am looking for some help. The vent for the gas hot water tank was flexible metal. I have not run into this before. Is it legal I am located in Washington state.

https://www.duravent.com/docs/product/TypeBgasvent_L820_2012-sept_w.pdf

They make single wall and double wall.

See if it has a tag that says it is suitable for type b gas vent. They do make them.