sewage tank

[Mark Savalla]

Hi, after 30 yrs of sail and two new knees, switched to a 86 , 42' MMC trawler.. Not much experience with large holding tanks, this boat, Pelican, has an electrical pump to pump out when past the 3mi. in the ocean. The pump is working but no sewage is coming out. I know the boat sat for 5 yrs. I am assuming the line is plugged. besides disconnecting the lines, is there anything I can try to unclog them? I have purchased some natural biologic that is supposed to loosen it but after a month nothing has changed.

 

[Gordon J]

What type of heads do you have. If vacuflush, you may have inverted duck bills on the discharge line

 

[Gmarr]

You need the Headmistresses book! Peggie Hall
The New Get Rid of Boat Odors: A Boat Owner’s Guide to Marine Sanitation Systems and Other Sources of Aggravation and Odor

 

[porman]

Is there a Y valve or a thru hull valve that needs to be opened?

 

[Peter B]

The pump might be one like I had that just would not self-prime in spite of claims it would. Don't ask what pains I had to go to to prime it. It was complicated...

 

[HeadMistress]

If the boat has been sitting for an extended period, there's a good chance that the tank VENT is blocked...most likely at the vent thru-hull because dirt daubers love to build their mud nests in thru-hulls.

Tank vents have two functions: they provide an escape route for air inside a tank displaced by incoming contents and a source of air to replace tank contents as they're drawn out. When the vent becomes blocked, preventing air from getting into the tank, the pumpout or overboard discharge pump pulls a vacuum that prevents it from pulling anything out. When no air can escape out the vent, the system becomes pressurized, which can cause anything from a geyser out the deck pumpout fitting to an eruption back through the toilet...even an imploded tank.

So...grab a screwdriver, ice pick or whatever works and scrape whatever you find in the waste tank thru-hull. If that doesn't solve your problem, we can explore the other possibilities. Meanwhile, don't use the toilet again...you don't want to pressurize the system.

 

[kchace]

Hi, after 30 yrs of sail and two new knees, switched to a 86 , 42' MMC trawler.. Not much experience with large holding tanks, this boat, Pelican, has an electrical pump to pump out when past the 3mi. in the ocean. The pump is working but no sewage is coming out. I know the boat sat for 5 yrs. I am assuming the line is plugged. besides disconnecting the lines, is there anything I can try to unclog them? I have purchased some natural biologic that is supposed to loosen it but after a month nothing has changed.

If its old and especially if its been sitting for so long the pump may be running, but the pump itself may have problems. Macerator pumps have rubber impellers which can fail. Diaphragm pumps have valves and the diaphragm itself can fail.

Ken

 

[Alaskan Sea-Duction]

So folks lets re-read the OPs post. It would seem he is referring to the macerator pump for pump overboard.


If the pump is running and you know there is stuff in the tank, it would seem the impeller on the pump may be bad. Depending on your system design, it may also involve moving the "Y" valve to the overboard position.


Dittos on Peggie's book! Get it.

 

[Mark Savalla]

Ok, thats a start, thanks for all the insight. I'll check the vent then, the pump itself.

 

[Maerin]

Macerator pumps are notoriously unreliable, I'd start there. As another post suggested, make sure there are no valves closed! Follow the line physically from tank to thru-hull. If it is a macerator, it will have a grinder blade and a rubber impeller. After that much time out of service, the impeller could be shot, the pump and any of the appurtenant piping could be fouled with dried debris. It may be informative to pull the hoses off the pump and inspect them to see what you're dealing with. If they're filled with dried stuff, you may be further ahead to just replace them. If you determine that the plumbing is clear, then a rebuild of the macerator will be helpful, if not required.

If you intend to use the overboard pumpout with any regularity, a macerator should be OK, the more frequently they're exercised, the more reliable it will stay. If reliability is a priority, then a diaphragm pump like a SeaLand will be more reliable, but it would require 1-1/2" hose & thru hull, and the macerator may only have a 1" thru hull; so switching to a diaphragm pump may not be easy.

You may consider pumping out the tank and doing a flush/rinse/repumpout before you start looking into the macerator and its piping. Lots easier than cleaning it out of the bilge!

 

[High Wire]

My boat has a Y-valve on the suction to the macerator to select pump-out via deck/shore fitting or macerator pump. Make sure its properly aligned. The only way to do that is to trace every inch of the flowpath. Some boats just have a T-fitting in place of the Y-valve that relies on the deck fitting having a good o-ring seal and tight.
Any air leak on the suction side can prevent the pump from working.

 

[FF]

Paper dried out in the pump can keep its valves from working.

I would purchase a new pump rather than rebuild the old one.

You might try disconnecting the suction to the pump and filling it with water and operating the pump.

This will see if the pump works , and might free the suction valve.

IF the pump is gravity fed it will last longer and work more often than one that has to suck up waste to get started.

The 120V units seem to last longer than the 12V units, not a big load for most inverters.

If a refit is required you might contemplate just a line from the tank to the deck fitting.

Then a 1 1/2 inch edson on a board can be used to dump when offshore.

Its far easier to live with a manual pump and some hose in a bag , than keep a seldom used poop pump in service.

KISS

 

[Mark Savalla]

Thanks to everyone, gives me the info for a planned organized attack.