Fred - I do not have an MKI. Mine is MKII and I do not know if they are the same set-up. However I will say that on my holding tank the pump-out is from the side and the hole is about 1" above the bottom. It goes to a "T" then directly out to the pump-out hose. The other leg of the "T" is where the macerator pump is attached. There are no valves to close. My macerator pump started to leak and I had much odor and you know what accumulated in my bilge a few days later. I washed and pumped it out. I am currently installing a new pump and a valve on the "T" where it goes to the pump. I will keep it closed except when I am ready to use the macerator. Yes there is not much room for me either but when the valve and the macerator arrives I will figure out how to put it together. So - it would be a good idea to add a vlave to the pump out so that you can close it in case it decides to leak. I will post photos after I complete my project.

We also have a Mk II but the discharge line comes right out of the back of the tank. I put a valve in the line to the macerator pump to be able to isolate it for when a condition like Haro experienced occurs. Not if it occurs, but when it occurs, because this stuff all breaks sooner or later. I see no reason why I couldn't have put a similar valve on the pump out line, other than it is a bit tight for space in there. It would keep effluent out of all but maybe 6 - 12" of hose I think.

When I replaced that tank outlet hose i tilted the boat to port side by pulling a line with a halyard to the next dock over to port. As the outlet is close to the center this raises the outlet a little relative to the bottom of the tank and sends any remaining stuff away from the outlet. I had no mess. The hose came off fairly easily and the new ones went on with a little soap and a little heat from a heat gun.
One trick. As the hose comes off the fitting hold your gloved hand over the end and peel that glove right off your hand and onto the hose...secure with a rubber band.

The holding tank arrangement on the Mk I versus the Mk II are completely different. I really think you need input (output??) here form some of the Mk I guys and gals.

I replaced the holding tank and all the hoses on my 1986 Cat 36 last season. The fitting that comes out of the tank at the bottom is barbed and is 1 1/2 " NPT thread 90 degree angle. The hose going to the pumpout/mascerator is the lowest part of the system. It will have fluid in it.

If you replace the holding tank at the same time (I would) the job is not that messy, because you can pull the holding tank out and make it lower than the hose, then detach the hose at the pumpout/mascerator junction and replace everything. To accomplish this, you need to cut out the fiberglass tabs on the plywood support structure and remove them. Then you can wrestle the holding tank - lower hose still attached - out of that spot and take the entire mess off the boat without spilling. As neilroach says - have something ready to put over that hose end when you remove it at the mascerator/pumpout junction.

I replaced everything in the system - all the hoses - the Y valve- and the mascerator - and the tank - Catalina Yachts has the tank in stock. My boat really needed a new system, and it improved the "aroma" in the cabin immensely.

If you want to put in a ball valve, measure the space where you plan to put it - it is a pretty tight spot on my Cat.

For all: if you have black sewage hoses on your boat, they are probably the source of any black water smells. The black rubber sewage hoses 'weep' sewage virtually invisibly.

I could not find the source of a bad aroma and couldn't believe the black hoses were the fault. Wiping them, touching them, they didn't *seem* to be the fault, but as soon as I replaced them with the white plastic hose the smell was no longer present.

Believe it.

Absolutely.....black hoses bad......white hoses good.....just don't skip one of them....replace every single one of them.

And "flush through" especially when leaving the vessel. Even the white sanitation hoses will break down eventually with uric acid working on them.

Fred

A couple of things that you might find helpful for your project are

1. when it’s time to start disconnecting hoses wearing a respirator mask with carbon filters such as the 3M 5000 series masks helps with the odor, not perfect but helps.

2. I like to use the Shields brand sanitation fittings because their hose adaptors are not barbed. This allows the hose to be removed in the future if necessary, I often find I have to cut a hose off a barbed fitting.

Replacing black rubber hoses with new white plastic hoses can be quite difficult because the white hoses don't have the elasticity of the rubber ones. I have tried heating the hoses with a heat gun, but with little improvement. Finally, I smeared silicone lubricant on the joints before pushing the hoses into place. It seemed counter-intuitive to me to lubricate something that one hopes will NEVER accidentally come apart, but that's what I had to do.

My experience heating the new hoses has been different than Larrys. I got the idea from a marine sanitation dealer in Seattle. He said that all the installers do it as necessary. The trick is to heat the hose slowly, evenly and just a little bit. If it is too hot to touch, that is too much. The point is to soften it just a little bit. Lube? I like liquid soap and know that it will have no chemical reaction with the hose or fittings.

Two comments. No, three:

1. Good on you for getting that old stuff outta there. The new sewage installation is going to smell sweeter than a baby's bottom. So to speak.

2. You work on your boat when it's 22 degrees F outside??? Holy cow. Am I a wuss or what? I am waiting until March when our temps get into the upper 50's.

3. Frank is personally selling Mk I holding tanks?

instead of using a heat gun to make the hose ends more pliable try dipping them into hot water for about 15 seconds; you can boil a kettle, have a coffee, and by the time you finish that the remaining hot water in the kettle will be just about right and there is no risk of overheating / deforming the hose....
I've just yesterday replaced our Raritan lectrasan with a new electroscan and replaced all hoses and Y valves etc. It took a day of swearing and cursing to get all the hoses run correctly but the hot water made the fitment of the hose ends real easy.

Hot water! That's the best idea I have heard so far. Thanks.

Good job on replacing everything. When you're done working with that 2" white sanitation hose be sure to keep a 2' piece aboard. That way, if you ever run into the guy who invented it, you can beat him to death with it. :D

PS - If you are replacing the diverter valve, feel free to check out the one I installed. It is a thing of beauty and located behind the head so you don't have to dig under the cushions to get to it or check it for leaks. Feel free to message me if you'd like more info. Or at [email]Homewest@socal.rr.com[/email] .

Mike