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Old 08-12-2019, 03:33 PM   #1
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Mainship 400 waste holding tank replacement

Anyone replace their holding tank?
I have crack (1/2 separation) on the side of the holding tank and it obviously needs to be replaced. I cant see how to remove the tank or put the new tank into place without tearing up the floor and creating a new structure for the floor above the tank. Would certainly appreciate if anyone knows a way to remove it & replace it without tearing up the boat? Thanks.
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Old 08-12-2019, 04:05 PM   #2
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Dont have any specific info on your Mainship, but when you get ready to order a new tank, I highly recommend Ronco. They make great tanks and have hundreds of stock shapes and sizes. They will put the fittings where you need them. If you need help cutting on your boat, I love cutting on other peoples boats...
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Old 08-12-2019, 04:32 PM   #3
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I see you've just joined us today...welcome aboard!

Removing the tank is the easy part if you have a Sawzall...putting a new one in is the only problem. The easiest solution for that may be a new location for the tank...boat builders almost always put 'em in the worst possible places...too far from the toilet or without any access to replace hoses when necessary etc.

As Dave said, Ronco Plastics Ronco Plastics marine Tanks is your best source for a new tank. They make TOP quality thick-walled water and waste tanks for a very reasonable price and have more than 400 shapes and sizes, over 100 of which are non-rectangular, and they install fittings in the sizes and locations specified by the customer when they make the tank.

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Old 08-12-2019, 07:54 PM   #4
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I see you've just joined us today...welcome aboard!

Removing the tank is the easy part if you have a Sawzall...putting a new one in is the only problem. The easiest solution for that may be a new location for the tank...boat builders almost always put 'em in the worst possible places...too far from the toilet or without any access to replace hoses when necessary etc.

As Dave said, Ronco Plastics Ronco Plastics marine Tanks is your best source for a new tank. They make TOP quality thick-walled water and waste tanks for a very reasonable price and have more than 400 shapes and sizes, over 100 of which are non-rectangular, and they install fittings in the sizes and locations specified by the customer when they make the tank.

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Peggie,
Ive looked at Roncos website and cannot find the size of the tank that requires replacement. The current tank is 48L x 23 1/4W x 9H.
Any suggestions?
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Old 08-12-2019, 08:07 PM   #5
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That is not an optimal tank size being only 9 tall. When you pump out and leave an inch or two that is a significant part of the tanks capacity. Is there somewhere else that you can get a taller tank. That way when you leave that inch or two it isnt as large a percentage of the tank.
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Old 08-12-2019, 08:26 PM   #6
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A correctly cut diptube can reduce the remainder to an inch at most...assuming that he has enough clearance above the tank for a diptube.

So, Todd...does your existing tank completely fill the space, or can you go a little higher and/or wider and therefore shorter... What make/model is the toilet? How many toilets? If more than one, are both connected to the same tank? If so, what's the distance from each?

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Old 08-13-2019, 08:10 AM   #7
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The existing tank essentially fills up the space. The area in the boat where the tank is located adjacent to the bathroom located underneath a hallway floor going from the master state room in the bow to the main cabin area. There is 1 toilet (Dometic) & 1 tank. The space the tank is located is 54L x 24W x 11H.
Tank has 5 access ports. 3 - 1.5 dia. ports on tank short end (towards stern) for pump out, macerator, & from vac pump from toilet. 1 - 1.5 dia. on top (towards stern) for tank fill gauge, which consumes approximately 1 of overhead clearance, and 1 - 0.5 dia. port on opposite short end (toward bow) for vent line. I see my only recourse is to cut out the floor directly over the tank and then build up a structure to support the floor over the new tank.
Any other insights or suggestions are welcome!
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Old 08-13-2019, 11:14 AM   #8
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Quote:
Originally Posted by Todd S View Post
The existing tank essentially fills up the space. The area in the boat where the tank is located adjacent to the bathroom located underneath a hallway floor going from the master state room in the bow to the main cabin area. There is 1 toilet (Dometic) & 1 tank. The space the tank is located is 54L x 24W x 11H.
Tank has 5 access ports. 3 - 1.5 dia. ports on tank short end (towards stern) for pump out, macerator, & from vac pump from toilet. 1 - 1.5 dia. on top (towards stern) for tank fill gauge, which consumes approximately 1 of overhead clearance, and 1 - 0.5 dia. port on opposite short end (toward bow) for vent line. I see my only recourse is to cut out the floor directly over the tank and then build up a structure to support the floor over the new tank.
Any other insights or suggestions are welcome!
Todd, I think you have correctly apprised the situation. I can't believe there is any way to get the tank out and then replaced without removing the floor above, if you want to put it in the same spot. I wish it were otherwise, I have the same boat but no cracks (yet) knock wood.
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Old 08-13-2019, 11:18 AM   #9
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Is the floor above the tank carpeted or teak and holly?

On tank replacements like yours, I cut a precise hole over the tank big enough to get the tank out, new in and have enough room to make connections.

I screw 1" X 2"cleats around the underside of the opening for the cut out floor to rest on.

Carpeted floors are easier but a teak floor can be made to look good around the opening. The teak flooring on production boats is usually a thin teak and holy plywood panel over 3/4" plywood. I rout the opening edges so teak trim, the same thickness can be glued down around the opening and lid to give it a finishing surround.

If increasing tank capacity, I make a cardboard or plywood mock up of the new tank to make sure it will fit in the space in addition to manuerving through doorways and halls.
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Old 08-13-2019, 11:28 AM   #10
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Same boat here as well. I'm afraid you, and me when my time comes, will have to cut out the floor.


A couple of thoughts.



1. Maybe go from the sender on the top of the tank with an internal float to a sender that attaches to the outside of the tank? I'm going to make this switch soon as my float is stuck and there is no access to the top of the tank. This would free up at least an inch of height and you could make the tank a little bit bigger.


2. Put in a much bigger vent line and run it forward to a through hull below the anchor locker. Or maybe two vent lines, on going forward and the existing one to the stb side.



3. Replace the hoses to the vac u flush tank and the pump out while you have the tank out. It will be the best access you ever get. They will need to be replaced anyway.


I wish you the best.
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Old 08-13-2019, 11:32 AM   #11
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Is the floor above the tank carpeted or teak and holly?

On tank replacements like yours, I cut a precise hole over the tank big enough to get the tank out, new in and have enough room to make connections.

I screw 1" X 2"cleats around the underside of the opening for the cut out floor to rest on.

Carpeted floors are easier but a teak floor can be made to look good around the opening. The teak flooring on production boats is usually a thin teak and holy plywood panel over 3/4" plywood. I rout the opening edges so teak trim, the same thickness can be glued down around the opening and lid to give it a finishing surround.

If increasing tank capacity, I make a cardboard or plywood mock up of the new tank to make sure it will fit in the space in addition to manuerving through doorways and halls.
I agree, make a neat cut to begin with. Make the hole as big as you can so you have room to work. I would also change the hoses while you are in there. Good luck. Any idea why the old tank cracked?
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Old 08-13-2019, 01:50 PM   #12
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Quote:
Originally Posted by Todd S View Post
The existing tank essentially fills up the space. The area in the boat where the tank is located adjacent to the bathroom located underneath a hallway floor going from the master state room in the bow to the main cabin area. There is 1 toilet (Dometic) & 1 tank. The space the tank is located is 54L x 24W x 11H.
Tank has 5 access ports. 3 - 1.5 dia. ports on tank short end (towards stern) for pump out, macerator, & from vac pump from toilet. 1 - 1.5 dia. on top (towards stern) for tank fill gauge, which consumes approximately 1 of overhead clearance, and 1 - 0.5 dia. port on opposite short end (toward bow) for vent line. I see my only recourse is to cut out the floor directly over the tank and then build up a structure to support the floor over the new tank.
Any other insights or suggestions are welcome!

If you haven't already, you might want to review this thread. Toward the end TooCoys posted a pic of their new tank, and it illustrates the flush fittings Ronco can include, and those can save you some headroom for top mounted innies and outies.

Time to replace the pooper!

Ronco can also make shorter dip tubes, compared to their standard solution, and we used those. There's pics of those too. I think it can get down to only needing about 2' overhead clearance...

In our project, switching from side-mounted to top-mounted fittings would have increased our capacity in the original tank by about 40%... and since we also were able to install a slightly larger tank, we eventually ended up with about a 60% increase in capacity.

-Chris
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Old 08-13-2019, 04:48 PM   #13
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I've been thinking about this. I think you can just open up the floor in the hallway and pull the tank out. You shouldn't have to cut out any of the floor in the fwd cabin.
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Old 08-15-2019, 12:19 PM   #14
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Thanks for all the great responses & the pics sent. Ultimately, the floor had to be cut out to remove the tank. Currently in process with installation of new tank.
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Old 08-15-2019, 01:50 PM   #15
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That's a heck of a crack. I wonder what caused it?
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Old 08-15-2019, 02:10 PM   #16
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When you replace the floor, I'd make it hatch (2 may be needed due the weight of just one long one)...to provide access to the tank to replace hoses etc. Use countersunk pulls.


This is very easy to do...I had two large hatches installed when I replaced

the sole in the galley and passageway between the galley and the dinette on my last boat.



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Old 08-15-2019, 04:45 PM   #17
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The issue occurred after the last pump out. I believe that the pump out vacuum did it. I assume it flexes under vacuum and became fatigued more and more with each successive pump out. Certainly the tank became concave, over time, on the large top. Ironically, the bottom was flat.

And yes, I will make floor over the tank easily removable so that the tank and all the fittings are easily accessible.
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Old 08-15-2019, 05:23 PM   #18
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Sounds like the vent may have been clogged. It might have created a vacuum in the tank and tried to suck it flat.
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Old 08-15-2019, 05:32 PM   #19
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Good point about vent being plugged. Chances are that was the issue. Im replacing all hoses as well as the vent line. I obviously will be more careful with that going forward. Thanks
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Old 08-15-2019, 05:34 PM   #20
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Since you are doing all that work, I would seriously consider adding a vent to the other side of the boat. Having a vent to each side of the boat will halp tremendously in getting oxygen into your tank. And don’t use vent filters.
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