It is quite possible...
...that your boat wasn't equipped with a holding tank. It should be fairly obvious if you have traced your plumbing and nothing is apparent to you. Holding tanks are frequently stashed under vee-berths, but as I recall the 30 is an aft head layout. It sounds like you have been crawling around your engine compartment. If you don't see any apparent tanks and furthermore, don't smell any ;-) then chances are you just have an illegal overboard discharge and need to add a tank. I looked at a 1979 Cape Dory that lacked one. Fortunately the supplies to add one aren't terribly expensive. I figured it would be about $300 for a ball park estimate, with the tank about 50% of that cost. The biggest pain is in performing the proper attachments. The hose (and be sure to by the best you can find) is thick and fairly rigid, making hose onto hose bard connections (of which there will be many) a royal pain.One of the pluses of my new boat was that the owner had just installed a new head and replaced all the hoses. However, one of the first things the surveyor noted was that there was a leaking connection. Not a big plus from my Wife's perspective!Bob