That doesn't help. If you double your capacity with a second tank, you have the same pressure. If you have two tanks with the same total capacity, you have even less pressure. In either case, it's not going to come out of any normal soaker hose or drip irrigation system. The only way to get more pressure would be to have more water capacity. It's the weight of the water that is supplying the pressure. How much water is needed to get an acceptable pressure? I don't know, but I can tell you that 305 US gallons is not even close to enough.