Holding tank discharge via thru-deck opening

[David B]

Originally Posted by peghall

...Much simpler to have the macerator pump (or manual pump) at the base of the toilet, pump up to the top of the tank....

Adding a macerator or manual pump to a toilet discharge does anything BUT simplify the system...starting with, it becomes a blockage in the toilet discharge line if it isn't operating simultaneously with the toilet's pump. If your toilet--manual OR electric--can't lift bowl contents up to 4", rebuild or replace the toilet...they're all rated to lift at least that high.

I don't think I made it clear enough - sorry. The macerator pump/manual pump I refer to is the only pump in the system - the pump that empties the toilet bowl.
This is by far the simplest system. Toilet contents are pumped out of the bowl up to the holding tank. Once in the tank, a single ball-valve on the seacock can empty the tank via gravity feed (when well out at sea), or when in port, the tank is emptied via a deck fitting and shore vacuum pump-out station.
No 'Y' valves, no pumps (manual or electric) and just a metre and a half of sanitation hose up to the tank from the toilet bowl, and a metre from the bottom of the tank straight to the seacock.
As to efficiency - I think we all understand the vacuum pump-out process is fairly quick (and painless as long as we maintain our tank breathers). The gravity emptying via the seacock is even quicker - literally just a few seconds, and the rush from the bottom of the tank down that big hose clears virtually all sludge out.

I understand that some boats for one reason or another have their holding tanks below water level, so for self-emptying at sea, they need to be pumped out. For that, I totally agree that one outlet for the deck fitting, and a separate outlet for the sea-discharge pump, is required - you don't want a pump in the deck suction line causing a restriction at best, or a blockage at worst.

In such an installation, I consider it even more important for the toilet to be fitted with a macerator pump, rather than a manual pump. You want the tank contents to be fully macerated before they sit in the tank waiting to be pumped out. A manual toilet pump doesn't do the job as well, and frankly, I find is more prone to blocking anyway. Manual pumps don't deal with great wads of toilet paper very well (I know - but despite what we say to our guests ......). I have experimented with an electric toilet, and it is surprising how much toilet paper that macerator pump will chew through, as long as there is enough water in the bowl - you wouldn't want to get your finger in the way !

As to maintaining the things, in my view/experience, a shaft seal is the most likely, and it's a 15 minute job to remove the pump from the base of the toilet (after flushing well with bio-disinfectant), replace the seal, and re-install the pump.

Anchors and toilets Hmm

[peghall]

You want the tank contents to be fully macerated before they sit in the tank waiting to be pumped out.

Actually, solid waste is at 75% water, and manual toilets do pretty good job of breaking it up,so it dissolves fairly quickly in the tank. And cheap single ply TP--which is what "marine/rv TP is, for a highly inflated price!--dissolves imto "snoiw" in water in an hour or less. So maceration is like a luxury car--nice to have, but not really necessary. Nor is maceration needed to dump a tank at sea...diaphragm pumps, both manual and electric (Sealand/Dpmetic, Jabsco and Raritan all offer electric diaphragn tank discharge pumps btw), work just find and there are no "lumps" unless somebody flushed something that's likely to clog a macerator pump. Nor would a macerator prevent the most common problem in gravity drain tanks: sludge that packs the discharge line because the tank it doesn't occur to owners to put a few gallons of water into an empty tank via the pumpout fitting--cuz that sends the water into the tank to stir up the sludge--to stir up the sludge and flush it out the thru-hull.

[David B]

Originally Posted by peghall

You want the tank contents to be fully macerated before they sit in the tank waiting to be pumped out.

Actually, solid waste is at 75% water, and manual toilets do pretty good job of breaking it up,so it dissolves fairly quickly in the tank. And cheap single ply TP--which is what "marine/rv TP is, for a highly inflated price!--dissolves imto "snoiw" in water in an hour or less. So maceration is like a luxury car--nice to have, but not really necessary. Nor is maceration needed to dump a tank at sea...diaphragm pumps, both manual and electric (Sealand/Dpmetic, Jabsco and Raritan all offer electric diaphragn tank discharge pumps btw), work just find and there are no "lumps" unless somebody flushed something that's likely to clog a macerator pump. Nor would a macerator prevent the most common problem in gravity drain tanks: sludge that packs the discharge line because the tank it doesn't occur to owners to put a few gallons of water into an empty tank via the pumpout fitting--cuz that sends the water into the tank to stir up the sludge--to stir up the sludge and flush it out the thru-hull.

Yes, I see no point in a macerator pump being used for pump-out. However getting a manual pump to handle wads (those guests again ) of toilet paper in the bowl is not as easy as a macerator pump chewing through it - in my experience anyway.
Water in the tank - plenty of it is good, but I can see the point if you have not emptied for some time via the gravity drain, the sludge might become a little compacted. The tanks I know have a suction outlet at the top pretty well in line with the gravity outlet at the bottom, so if you were lucky, a hose down through the deck fitting would find it's way into the gravity feed and right down to the seacock (and if not, then there is always the inspection port .....).
Keep things moving in there and 'fresh' is the way.
Out of interest, what do you suggest for winterising an electric toilet. We have had a macerator pump on one of the toilets suffering from crevice corrosion on the shaft just in front of the lip-seal, and it can only have happened during winter lay-up, with the last F/W flush and disinfectant sitting around the shaft for 9 months.

[peghall]

Out of interest, what do you suggest for winterising an electric toilet. We have had a macerator pump on one of the toilets suffering from crevice corrosion on the shaft just in front of the lip-seal, and it can only have happened during winter lay-up, with the last F/W flush and disinfectant sitting around the shaft for 9 months.

Antifreeze poured into the bowl just goes out the pump discharge...protecting only the toilet discharge and the tank. To winterize the WHOLE system, remove the intake hose from the thru-hull (prob'ly be a good idea to close the seacock first)...flush the toilet as dry as you can get it without frying the impeller... and stick the intake hose into a gallon jug of non-toxic propylene glycol antifreeze ("the pink stuff")...flush the toilet long enough to pull the whole gallon all the way to the tank...through the intake line, the pump, the channel in the rim of the bowl AND the discharge line and tank. Do it essentially the same way to winterize manual toilets.

If your toilet is one that's designed to flush using onboard pressurized fresh water, you only need to add antifreeze to the bowl and flush...winterizing the fresh water system takes care of the rest.

[David B]

Originally Posted by peghall

Out of interest, what do you suggest for winterising an electric toilet. We have had a macerator pump on one of the toilets suffering from crevice corrosion on the shaft just in front of the lip-seal, and it can only have happened during winter lay-up, with the last F/W flush and disinfectant sitting around the shaft for 9 months.

Antifreeze poured into the bowl just goes out the pump discharge...protecting only the toilet discharge and the tank. To winterize the WHOLE system, remove the intake hose from the thru-hull (prob'ly be a good idea to close the seacock first)...flush the toilet as dry as you can get it without frying the impeller... and stick the intake hose into a gallon jug of non-toxic propylene glycol antifreeze ("the pink stuff")...flush the toilet long enough to pull the whole gallon all the way to the tank...through the intake line, the pump, the channel in the rim of the bowl AND the discharge line and tank. Do it essentially the same way to winterize manual toilets.

If your toilet is one that's designed to flush using onboard pressurized fresh water, you only need to add antifreeze to the bowl and flush...winterizing the fresh water system takes care of the rest.

Thanks for that. I had not thought of using antifreeze (freezing is rare in the Med), but it would have anticorrosive properties also. I am thinking at some stage we will convert to F/W flush (perhaps with a 'Y' valve even !!! - so that we can still use seawater if required)). As an interim, I could install a flushing port right at the seawater inlet.

Always something to do on a boat, but that's a good thing.

[peghall]

Originally Posted by David B

... I am thinking at some stage we will convert to F/W flush (perhaps with a 'Y' valve even !!! - so that we can still use seawater if required)).

Big no-no because you'd risk contaminating your fresh water system with sea water, or worse yet e-coli or or other bugs from the toilet bowl. Raritan has a system they call "Sea/Fresh" that has all the necessary vacuum breakers, switches are relays needed to switch between sea water and fresh, but it's very pricy and only works with high end models designed to use pressurized fresh water and requires a separate remote intake pump of sea water.

As an interim, I could install a flushing port right at the seawater inlet.

That could work...or, there's an even easier way that works on most boats that have below-waterline sink drains and the head sink and toilet are on the same side of the keel:

Re-route the head intake line to tee into the head sink drain line (this will leave you with an unused thru-hull)...the tee needs be below waterline, as close to the seacock as possible. Most of the time, you'll flush normally using sea water...but any time the boat will sit, or just as often as you feel the need to rinse out the system-or just find yourselves in water you don't want to use--close the thru-hull and fill the sink with clean fresh water...flush the toilet. Because the thru-hull is closed, the toilet will pull the water out of the sink, rinsing out the whole system--intake line, pump, channel in the rim of the bowl and the discharge line. You can use the sink to add antifreeze...white vinegar to prevent mineral buildup.... It MAY be necessary on some boats to keep a plug in the sink except when using it, to prevent the toilet from pulling in air when the seacock is open. That depends on how close to the waterline the thru-hull is, heeling etc.

Btw...some boat builders--Tartan was one--used to use the same thru-hull for the head and head sink...it works well! And a lot easier to use than having to mess with a "flush" line tapped into the intake line somewhere.

[Captain Bill]

Originally Posted by David B

Yes - a large outlet at the bottom of the tank for gravity discharge. Works very well.

This only works well if you can use this method fairly often. I once tried to drain my tank after having been in an area where I could only pump out for two years. In the meantime sludge at the bottom of the tank took advantage of that gravity you are looking to take advantage of and settled into the discharge tube and over a two year period packing itself into something strongly resembling concrete. Needless to say nothing drained when I was off shore with a full holding tank. I managed to pump most of it over the side through the deck fitting, but not all of it. Needless to say the repair ended up being a very shitty day.

[David B]

"Big no-no because you'd risk contaminating your fresh water system with sea water, or worse yet e-coli or or other bugs from the toilet bowl. Raritan has a system they call "Sea/Fresh" that has all the necessary vacuum breakers, switches are relays needed to switch between sea water and fresh, but it's very pricy and only works with high end models designed to use pressurized fresh water and requires a separate remote intake pump of sea water".

Yes, a non-return valve would be the minimum required there of course. Safest is a separate flush tank, but then it gets too complicated/too space-hungry. I like your idea of using the sink as a feed for winterising fluid. On both our heads we have separate feed-pumps from separate through-hulls, but nothing to stop putting a link across via a 'Y' valve feeding from a 'T' on the basin drain. I will look into this when we are next on board.

Originally Posted by Captain Bill

This only works well if you can use this method fairly often. I once tried to drain my tank after having been in an area where I could only pump out for two years. In the meantime sludge at the bottom of the tank took advantage of that gravity you are looking to take advantage of and settled into the discharge tube and over a two year period packing itself into something strongly resembling concrete. Needless to say nothing drained when I was off shore with a full holding tank. I managed to pump most of it over the side through the deck fitting, but not all of it. Needless to say the repair ended up being a very shitty day.

Yes, that's a long time to not drain the sea line. Here's one idea - a small tube going right down just short of the seacock, with an air pump feeding it. That would keep the sludge in there from compacting, and also ensure the tank remains aerobic.
It's all getting too complicated now - just put a ball-valve right at the outlet of the holding tank to keep the drain-line clear until emptying (assuming you can get to that area easily).

[jamhass]

OK, I know I am late to this discussion but internet is sometimes rare when cruising offshore ...

To the original issue of pumpout via the deck fitting:

We've been doing this for years now. Screwed a manual Whale diaphragm pump to a piece of plywood, added some clear reinforced hose, a few nylon pipe fittings of appropriate size and all is well. Discharge hose is long enough to reach the water so black water stays off the hull. We only discharge off shore underway, and the entire operation takes 15 minutes, including setup, pump and a thorough flush with the deck wash. No issue with smelly hoses, as I use pipe caps on the ends for stowage.

Boat originally had a system to pressurize the holding tank for discharge and I thought that was a really sh%$#y idea and pulled it out.

[David B]

Originally Posted by jamhass

OK, I know I am late to this discussion but internet is sometimes rare when cruising offshore ...

To the original issue of pumpout via the deck fitting:

We've been doing this for years now. Screwed a manual Whale diaphragm pump to a piece of plywood, added some clear reinforced hose, a few nylon pipe fittings of appropriate size and all is well. Discharge hose is long enough to reach the water so black water stays off the hull. We only discharge off shore underway, and the entire operation takes 15 minutes, including setup, pump and a thorough flush with the deck wash. No issue with smelly hoses, as I use pipe caps on the ends for stowage.

Boat originally had a system to pressurize the holding tank for discharge and I thought that was a really sh%$#y idea and pulled it out.

Good that that this works for you, and the caps on the pipes is certainly well worth while. For us, I still prefer the 4-5 second (literally) opening of the seacock to a 15 minute pumping procedure. But then we are gravity feed, and if yours is below the water line then that is a different story. We all have our ways it seems.

[peghall]

This only works well if you can use this method fairly often.This only works well if you can use this method fairly often. I once tried to drain my tank after having been in an area where I could only pump out for two years. In the meantime sludge at the bottom of the tank took advantage of that gravity you are looking to take advantage of and settled into the discharge tube and over a two year period packing itself into something strongly resembling concrete.

So what was stopping you from putting a couple of inches of water into the tank after pumpout and opening the thru-hull every couple of months???