Looking for a specific plastic bag type

I am working on a project that needs a large collapsible water reservoir. I am thinking a kind of heavy duty plastic bag

kinda like this

I dont mind if its a wear part that gets replaced every few uses but it needs to hold at least 30-40 gallons of water without bursting easily for a couple days of sitting full (would not move around so sloshing not an issue).

any reccomendations as to a proper search term or a possible solution?

It would be supported around the top for filling/standing

Search for bladders. There is a 40 gallon RV bladder for $100 as one of the first hits on google. Tou wont need to keep replacing them, either.


I kinda needed something “open topped” which a link off of a site looking at bladders got me to this

which I think will do nicely.
thank you!