You better start with your boat and model year. Lots of years have different systems. If you have a GIII sprinkler valve system you need to look for the manifold with the 3 valves that open to fill the 3 bags. It looks like this:
You can take the valves apart and clean them out. They are very simple. You can buy replacements at Home Depot for about $15. Take pics, ask questions. Don't be afraid. This is very simple stuff even for the non-mechanically inclined. It's just a water pump and a valve that opens. If the valve is sticky it stays open and fills all the time. You want the valve set to closed so it only opens when energized. You'll be fine.