Peggie,I am in the process of installing a new holding tank (the prev owner had one of those flexible bladders, which was starting to leak – yuck!). I have followed your book and postings of others and think that I have a good plan.My setup is as follows: 1975 Pearson 26, WC headmate, thru-hull intake. From the exit of the head, there is a vertical run of hose to a vented loop, then to a Y-valve. The exit thru-hull is still plumbed, though being in the Chesapeake, we do not use it. The hose to the thru-hull is about 3 feet long, while the hose to the holding tank is about 5 feet long. I am ordering a 9 gal. ronco tank with a dip-tube for pump-out. Now for my problem...When the head is in flush mode, the pump handle is easy to operate, water is drawn into the bowl, etc. When you move to dry mode, the pump handle becomes more difficult to operate, until a certain point where it seems that you have moved the water up past the vented loop. Because my holding tank is not yet installed, I opened up the exit thru-hull to push some raw intake water through the system (shh...). I noticed the _same_ resistance of the pump handle. This would seem to point to the vented loop as the clog, vs the holding tank vent.Somehow, though, it doesn’t make sense. I can’t be pressurizing the vented loop, even if the vent isn’t open. The head doesn’t fill with water if left in pump-dry position, but could there be a clog or something in the head discharge hose?Thanks for all your help!Also, would you recommend a clean-out inspection port on the top of the holding tank, or is this not necessary?DavidPS. I know that I should re-build the head, but there are so many other projects!!!