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chuck g 08-03-2010 05:34

Holding Tank Configuration Question
I'm in the midst of installing a new holding tank; my plan is to send macerated waste directly to the tank and from there use a manual diaphagm pump to empty the waste when I'm legally able to do so. I'll also have a separate pumpout capability.

My dilemma is that the seacock I'll be using is shared with a sink drain in my head. I want to be sure I'm not going to have fumes from the holding tank discharge coming back into the boat via this route. Originally I was going to use a straightforward Y-valve to bring the two discharge lines together before the seacock, but now I'm wondering if I should install something more specialized for this application. Haven't been able to find such a thing in my online wanderings; any advice would be appreciated.


Pete7 08-03-2010 06:12

Chuck, is the seacock below the waterline? if you pump the waste tank could it end up in the sink as the path of least resistance? The Memsahib will be please with you if that happens :whistling:

A separate seacock would ensure you only discharge when you want to, not if the pump starts to leak waste overboard.

It is a job I have planned too, but I have two seacocks (sink and shower) next to each other so plan to drill out one for waste and plumb the shower and sink together in the other.


gonesail 08-03-2010 07:17

your plan sounds the same as what i am doing. head direct into plastic tank with on deck and overboard pump outs ... but i am putting in an electric waste pump. i would say that you need another thru hull for the holding tank. do you have a vented loop?

chuck g 08-03-2010 07:20

In answer to the questions, the seacock is below the waterline and I do indeed plan on a vented loop. I'm not a fan of drilling unnecessary holes below the waterline, so as I ponder this issue, I find myself thinking that perhaps I should just tie in the discharge for the sink in the head to the one for my galley sink... thoughts?

Mule 08-03-2010 07:21

Throw out your holding tank, get rid of your existing toilet, put your connecting hose in the dumpster, clean up and list your maserator. After you do that reclaim the holding tank space for other uses. Then put in a natures head and be done.:thumb:

jkleins 08-03-2010 08:22

In the setting of direct connection of the head to the holding tank and then a separate connection for the holding tank to the throughhull via a pump (which sounds like what is being talked about) what would a vented loop do and why would you use one? Wouldn't you only open the throughhull when pumping out? Is that not good enough to prevent ingress of water?


gonesail 08-03-2010 08:48

agree you could do without the loop and just open the thru hull when pumping out .. it would simplify things a lot and avoid the possibility of leaks and odors from the vent. also the manual and electric pumps have joker valves in them.

Sailmonkey 08-03-2010 08:58

What's wrong with just installing another thru-hull fitting in the boot stripe? That way you don't have another below waterline hole. Cats seldom have head discharges below the water line either.

peacheykeen 17-03-2010 17:16

A Y valve to the drain, to serve the sink and the holding tank will work. I did the same configuration, put the manual pump above the water line . The Y valve "seals the sink drain from the tank output hose. Presume that you'll throw the Y valve, pump out the tank and put it back into "sink" postion or the tank may fill with sea water.

Captain Bill 17-03-2010 18:06

What ever you do do not come directly out of the bottom of the tank into a vertical pipe. Solids from the tank will pack in the pipe and you don't even want to know what you have to do to get them out. In the meantime if your off shore and don't have a pumpout available you'll have a full tank and no way to empty it. I know this from experience.

CarlF 17-03-2010 18:11

Another option - Use the seacock for the holding tank and install a shower sump to drain the sink at a new bootstripe thru-hull. (I'm assuming that the sink can't gravity drain to a bootstripe thruhull - the best solution)

Pro: Since the head seacock will only be open when you are pumping the holding tank, it is no longer a sinking risk. Since it is only used for the holding tank, it is convenient to wire tie it to make the Coast Guard happy. No vented loop is needed in the line (including between the holding tank and head) since the holding tank has a vent. Should put one in the shower sump line.

Con: Shower sumps are an added complexity and point of failure (although it's an inconvenient rather than dangerous failure). A Whale 800gph shower sump with pump is less than $100. A spare pump and switch for when it breaks is less than $50.


Jentine 17-03-2010 18:21

Are you daft man? Do you brush your teeth in the toilet? Why would you want to connect your toilet to the sink where you perform cleaning functions? They must remain separate for sanitary reasons. Plumb the sanitary tank discharge through its own seacock. Since you are so close to the ocean and I assume you normally sail offshore more than three miles, I would recommend that you install a Y valve to direct the waste either to the tank or to directly overboard. It is not reasonable to pump everything into a tank, only to later discharge it overboard.
The pick-up for the overboard discharge pump is an additional line that would be plumbed into the overboard discharge below the Y valve.

Chief Engineer 17-03-2010 18:38

Jentines' reply is spot on.

Howie mandel (a noted germophobe) would have a stroke!!!!!

The smell for one....the remnants creeping up the hoses.

I really don't understand why people are such hole-a-phobes,,,,

jkleins 19-03-2010 05:08


Originally Posted by Jentine (Post 420632)
It is not reasonable to pump everything into a tank, only to later discharge it overboard.
The pick-up for the overboard discharge pump is an additional line that would be plumbed into the overboard discharge below the Y valve.

I disagree. I think it is perfectly reasonable to pump everything into a tank and then out when desired. For several reasons:
1) This allow you to keep the seacock closed at all times except for the minute or two that you are watching it while pumping thus reducing the chance of a hose failure and leak.
2) The urge sometimes occurs when you are closer then 3 miles in and why have to think about changing the Y-valve setting when you really need to go.
3) Y-valves are a source of failure and maintenance.
4) Having the Y-valve does not allow you to eliminate any other part of the system as you still have to have all the others unless you are comfortable using a pump-out all the time for your holding tank.
5) Not having a Y-valve allow the output hose from the toilet to have no connections all the way to the holding tank. This reduces the corresponding points of potential clogging hopefully reducing chances of failure.
6) Having a Y-valve usually means you have to locate it somewhere accessible which can just give you more hose to potentially leak, clog or break.
7) If you have the throughhull open while sailing it is prudent to have a siphon in the system to prevent backflow into the toilet which again just complicates the output hose of the toilet by creating a loop that holds sewage and increases potential smell and clogging.

Just my opinion. There may be other reasonable options but having the simplest system you can design should be included in with them.


gonesail 19-03-2010 05:59

the other problem with the overboard y-valve is that the law says it needs to be secured. so unless you are offshore for extended periods it could be awkward and maybe difficult to keep up with this. in other words you might just leave it secured all the time .. in that case you may as well pump direct to the holding tank and not worry about it .. like Jim said above.

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