PVC is not recommended for use with compressed air.
I'd be surprised if you can find a pressure-rated
PVC tank (or even of polyethylene).
There are equations for the basic characteristics of water jets from nozzles out there. (I don't have them. You might be able to find them on the internet or maybe in a water hydraulics
book.) In any case, you should be able to find an equation that correlates the nozzle/hole diameter to the pressure and velocity and height of the water jet will reach.
Also, that information will give you a better idea how much pressurized water you really need since it will give you the flow rate per nozzle and then you know how long you want each nozzle to operate (Did you really mean 3-inch diameter on your tank?). (A 3
foot diameter tank as described has about 100 gallons of water for a working capacity.) At 2.5 feet of water in a 3
foot (?) diameter tank, that's 1,100 lb of water to move.
Note that if you just "charge" (rather than have a constant air compressed air supply) an acceptable tank with compressed air, the pressure will
drop by a factor of 2 (at least) as you spray out most of the water. (Although I can't imagine having to spray that full 100 gallons.)
(ricc0luke's suggestion of a pressure tank is probably the best – look in a plumbing supply catalogue – these types of tanks are typically used in houses with individual wells and tall buildings. They are made to be pressurized. [For some reason, I think these tanks have an internal rubber bladder that allows them to be pressurized by the well pump – you may be able to pressurize your tank with the venues water pressure.] And consider the pressure of your source of compressed air and the design pressure of your
system [that is, assume that the entire system might be pressurized to the source's maximum pressure] – the weak link will be the tank/pipe joint or a valve.)
Again,
PVC is not recommended for use with compressed air.
Joe