Good advice from Dansy. Be careful with fast fueling rates. 5psi is a lot .. it is easy to fracture hard-walled tanks (e.g. fiberglass, or especialyl kevlar).

The thing to remember is that the problem typically comes from the vent lines .. when they have air in them, they can support a high filling rate. Once the tank fills (or the first tank fills and it starts on the second "in-series" tanks) there is liquid in the vent lines and the pressure can build VERY fast. This can occur with series-connected tanks in the jet, or with the overflow tank. A variable speed pump is great and if you can baby sit it, you can go fast when the vents have air in them, and then slow down.

I've done a lot of work building fueling stations so have instrumented all this on the bench...

Dave