I suppose your reason for using an outdated 1958 toilet was to save money. Understandable, but this toilet requires at least 3.5 gallons of water to fill, and very possibly as much as 5 to 7 gallons! A new low flow toilet such as the Toto Drake II would require only 1.28 gallons of water. Perhaps saving water isn't a major concern, but think about how much stress you are putting on you septic system. I would suggest that rethinking the cost of a decent quality toilet is in order. BTW, a pressure gauge is cheap and easy to use.