I have an old built in fiberglass tank that was used to hold Kerosene for a heater and stove that were removed years ago. Its location would be perfect for the holding tank I need to replace, directly below deck pump out and adjacent to the head, unlike the existing tank. The tank has been full for years without any sign of leakage. Can I just use it as is, with the addition of needed fittings of course, or do I need the replace it? Thanks