I have an older millivolt natural gas boiler. I used to have an expansion tank that was aprox 2 ft long by 15 in, in diameterand when it got too full I just hooked a water hose to it and drained it, it worked well, but it got a hole in it so I had to replace it.The one the plumber sold to me was the smaller air precharged one . The pressure really fluctuates between 5 psi (when cold) to 25 psi (when hot). The old one never done that. Can I still get the older style tank or do you have eny other recommendations