Hidden grinder pump behind Waynes Coating

Unfortunately, you most likely can't do anything about this now. First, the only thing which might have been able to do--that is, the only cause of action you might have had--would have been for fraud: for making a material (significant) misrepresentation (or lie) about something not readily or normally discoverable during the home inspection. However, that can be difficult to win at the best of times, since you have to show that the seller knew this was a problem and deliberately (or logically must have deliberately) hid it. But if, for example, it could have been installed by their predecessor, so that they did not even know about it, or they knew, but it was simply not a problem in any way while they owned the home so that there'd be no logical reason to disclose it (the seller does not need to disclose *everything* they know about a house--just the problems or reasonably likely potential problems), then they would not have committed fraud by a failure to disclose. Only problems or likely potential problems of which they were aware but hid may be fraud.
Second, the statute of limitations, or time within which you must sue, in your state for fraud is only 3 years, not 4. After 3 years, you can't bring a fraud case. While there are sometimes ways to "toll" or extend the statutue of limitions, to get more time, such as if there was no reasonable way to have possibly known of the problem earlier, it is  not a given you'd succeed: the presumption is that after the statutory period has expired, you can no longer sue, so a court could hold you to a strict interpretation of the statute of limitations, precluding the suit.