It sounds to me like your hoses have finally given up the ghost. I replaced all the hoses from the head to the thru hull with hose from West Marine. I don't remember what it was, but it was a solid white hose instead of what looked like vacuum cleaner hose that was on the boat when I bought it. I have yet to replace the hose coming from the holding tank to the pumpout fitting since I haven't been able to make the sharp bend as was done originally. My latest thought is to try and find some sort of J-tube made from hard plastic and splice it in where the the hose makes the u-turm coming out from the aft, bottom of the holding tank. So far, I haven't been motivated enough to try and hunt one down though. Also, you will probably find that the hose from the head to the vacuum breaker, to the Y valve will all be the same size. The thru hull nipple is about 1/8 inch larger diameter. I ended up heating the hose in boiling water to soften it up enough to get it over the hose barb. By far the hardest part of the job. The manufacturer of the hose does not recommend heating it to make it fit, but I haven't had a problem in the three years since I have done the replacement. Good luck! Changing the hoses should do the trick. (You won't believe the crap you will find in them either!)
