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Old 10-11-2014, 09:50   #1
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Holding Tank Pump Out

Currently the only way to empty my holding tank is to pump it out at a station.
I was thinking though that I could put in a diaphragm pump off a T from the pump out hose and connect it to the current thru hull, without any valves?
My idea is that with the cap on the pump out fitting, the pump could only pull from the tank so I don't need a valve there, and the valves in the pump would prevent back flow when I pump out regularly.

Why won't this work?
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Old 10-11-2014, 10:05   #2
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Re: holding tank pump out

The concept worked for me, but I also had a Y valve so I could discharge directly from the head when I was not in port.
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Old 10-11-2014, 10:44   #3
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Re: Holding Tank Pump Out

I have a seacock now, open it and the tank is bypassed, close it and the liquid is pumped up hill and into the top of the tank, thought was to leave that alone, but T into it and be able to pump the tank, the head Joker valve would prevent back flow, or I think it would unless of course the thru hull colgged, in that instance I'm pretty sure pump pressure would overcome the Joker valve.
I just dont want to install two Y valves if I don't have to, additional failure points, cost and room
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Old 10-11-2014, 10:46   #4
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Re: Holding Tank Pump Out

It sounds good in theory but I have no idea how much suction a pump out station would put on the system.

Wondering if the flapper valves inside the diaphragm pump would stand up to that much suction.
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Old 10-11-2014, 11:10   #5
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Re: Holding Tank Pump Out

Mine is tee'd to a diaphragm pump and a through hull. I've only used the pump overboard part of it rarely (trips to B.C.), maybe 20 times, over the 8 years it's been installed. Rest of the time I go to the pumpout. It has always worked.

I don't know if it helps for the check valves, but I keep the seacock closed to try to limit the pressure differential across the valves.
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Old 10-11-2014, 12:08   #6
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Re: Holding Tank Pump Out

Quote:
Originally Posted by a64pilot View Post
Currently the only way to empty my holding tank is to pump it out at a station.
I was thinking though that I could put in a diaphragm pump off a T from the pump out hose and connect it to the current thru hull, without any valves?
My idea is that with the cap on the pump out fitting, the pump could only pull from the tank so I don't need a valve there, and the valves in the pump would prevent back flow when I pump out regularly.

Why won't this work?
Rather than counting on the cap on the pumpout fitting to maintain a vacuum, place the T where the discharge hose leaves the holding tank (at the bottom of the tank). You will be sucking sewage and won't need a vacuum. My tank has two outlets but one outlet and a "Y" would work as well. A "Y" fitting will present less resistance to sewage than a "T". There's no need for a valve.

I'm not sure what you mean by "the current thru hull", but you can't share the discharge from your holding tank with another function. If you locate the discharge thru hull above the water line you don't have to worry about loops and anti siphon devices.
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Old 10-11-2014, 12:40   #7
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Re: Holding Tank Pump Out

Mine is teed into the pump-out line without a Y valve. When using a pumpout station, the thru-hull after the macerator is closed and therefore the tank gets sucked out. The pumpouts in my marina suck enough to drain the toilet bowl - i.e. I don't have enough vent to prevent that.

Put the deck fitting on, open the thruhull after the macerator, and I can drain the tank with the macerator.

You won't put too much suction on the gusher pump, the thru hull will be closed .
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Old 10-11-2014, 18:52   #8
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Re: Holding Tank Pump Out

A64pilot,

Joker valves get tired and quit functioning. Don't rely on one unless you want to cope with the ensuing mess. They're not too much fun to change.

Ann
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Old 11-11-2014, 06:00   #9
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Re: Holding Tank Pump Out

Our holding tank has two outlets, one to the deck fitting (for pump out at a shore station) and one to a macerator which leads to a thru-hull with its own seacock (for offshore emptying where legal).

The macerator pump does not impede backflow. If I leave that seacock open, the holding tank (and eventually the head) will fill with sea water.

-Chris
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Old 11-11-2014, 06:08   #10
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Re: Holding Tank Pump Out

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Originally Posted by ranger42c View Post
Our holding tank has two outlets, one to the deck fitting (for pump out at a shore station) and one to a macerator which leads to a thru-hull with its own seacock (for offshore emptying where legal).

The macerator pump does not impede backflow. If I leave that seacock open, the holding tank (and eventually the head) will fill with sea water.

-Chris
We have the same problem with our aft holding tank, which is below water level. The forward one which is above the water line, doesn't. And, of course, the through hull for the aft macerator discharge, on our boat is hard as hell to get to, while the forward is very easy to get to.
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Old 11-11-2014, 06:24   #11
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Re: Holding Tank Pump Out

I'm still at a loss as to what to do, who would have thought something this simple could have so many possibilities?
I think I'll end up with the front head as direct discharge to keep the hose run short and simple and therefore easy to replace, and only connect the rear head to the holding tank, have it discharge into the tank, no bypass, but have a diaphragm waste pump ( not a macerator) to empty it as well as being able to pump it out.
Does the law stipulate all heads have to be connected to a holding tank? I know you have to have a holding tank, in my plan the fwd head would not be used when we needed the holding tank is all, so we will not be discharging when we aren't supposed to.
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Old 11-11-2014, 06:31   #12
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Re: Holding Tank Pump Out

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Originally Posted by Ann T. Cate View Post
A64pilot,

Joker valves get tired and quit functioning. Don't rely on one unless you want to cope with the ensuing mess. They're not too much fun to change.

Ann
I've changed them before, I've actually just converted both heads to "fresh heads" wasn't nearly as bad as I thought it might be, but I did flush a lot of soapy water through everything first. The Fresh Head uses a different type of Joker, rather than being sandwiched between two flanges as normal, it's part of a rubber sleeve that is attached on both ends by hose clamps, much easier to R&R.
I'm trying to keep it simple, and the above plan is the simplest I can come up with.
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Old 11-11-2014, 07:14   #13
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Re: Holding Tank Pump Out

I think your plan will work. My boat has a similar set up except I use an electric macerator pump. The toilet flushes into the tank. The tank has a tee on the discharge fitting. One line from the tee goes up to the deck and the other goes to the pump. The discharge from the pump goes to the seacock. This set up seems to work fine for either dockside pump out or overboard discharge.
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Old 11-11-2014, 07:23   #14
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Re: Holding Tank Pump Out

Is a diaphragm pump more reliable than a macerator?
Assuming I use plenty of flush water, will a diaphragm pump discharge a holding tank reliably?
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Old 11-11-2014, 07:36   #15
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Re: Holding Tank Pump Out

"Is a diaphragm pump more reliable than a macerator?"

Yes, especially a nice big manual diaphragm pump.
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