Holding tank pump out

[grahamdouglass]

I have a question regarding holding tank pump out.

When I go to use the pump out to empty my tank, the suction hose empties the tank and proceeds to suck water up through the ocean discharge and pumps sea water. I usually pump out at sea with my macerator and ocean discharge before going to my club because I like to fill my tank with fresh water. But last time I forgot and I have a partially filled tank.

Question. If I were to shut my ocean discharge, fill my holding tank with fresh water and then pump, would the pressure cause any problem to my jabsco head? Should I suction my holding tank on dry bowl or wet? Does it make any difference?

Give me your thoughts on this. What is the general consensus in pumping out the head, using cleaning products prior to pumping out, using fresh water flushes while pumping out, pumping out with the ocean discharge open or closed etc.

 

[CharlieO.]

I do not have an overboard discharge. Head to holding tank to pump out. Pump out works just fine.

 

[mvweebles]

I have a question regarding holding tank pump out.

When I go to use the pump out to empty my tank, the suction hose empties the tank and proceeds to suck water up through the ocean discharge and pumps sea water. I usually pump out at sea with my macerator and ocean discharge before going to my club because I like to fill my tank with fresh water. But last time I forgot and I have a partially filled tank.

Question. If I were to shut my ocean discharge, fill my holding tank with fresh water and then pump, would the pressure cause any problem to my jabsco head? Should I suction my holding tank on dry bowl or wet? Does it make any difference?

Give me your thoughts on this. What is the general consensus in pumping out the head, using cleaning products prior to pumping out, using fresh water flushes while pumping out, pumping out with the ocean discharge open or closed etc.

As long as vent to tank is not clogged, should be fine.

Peter

 

[Bacchus]

"When I go to use the pump out to empty my tank, the suction hose empties the tank and proceeds to suck water up through the ocean discharge and pumps sea water."

I'm not sure if you meant this as a statement or question?

1) O'board discharge should not be left open, especially anywhere you would pumping out as it would be a NDZ.
2) I doubt you will ever be able to draw raw water back in when pumping out as holding tanks are vented and you will draw air in when pumping out thus eliminating the ability to draw a vacuum on the tanknsufficient to draw in raw water.
3) Same holds true for ability to draw water through the head... not likely due to tank vent

Yes raw and/or fresh water flushes of tank is a good practice following a pump out. IMO Several partial tank fulls more effective than one full tank.

 

[ranger58sb]

Overboard discharge should always be closed unless you're using it.

In some boats, leaving that open will fill the holding tank even wthout suction from the deck pump-out fitting.

As long as your vent line is clear, suction will not damage the toilet. (I suspect probably won't, even if the vent line is NOT clear. In that case, the toilet would be acting as the vent source.)

-Chris

 

[Gdavid]

Sounds like your vent line is clogged for this to happen in the first place. Your discharge thru hull should be closed when not in use, whick would prevent this as well but something is off with your vent line

 

[backinblue]

I have found that if I accidentally leave my discharge open, the holding tank will partially fill with sea water because the tank is partly below water level. Surpiesed that the macerator pump allows this but it does. Could be because of the strong current flowing under my hull pushing water inside. Normally the overboard should be closed and pumpout should be fine as long as the tank vent is clear as others have said.

 

[mvweebles]

I have found that if I accidentally leave my discharge open, the holding tank will partially fill with sea water because the tank is partly below water level. Surpiesed that the macerator pump allows this but it does. Could be because of the strong current flowing under my hull pushing water inside. Normally the overboard should be closed and pumpout should be fine as long as the tank vent is clear as others have said.

Shouldn't there be a vented loop between macerator and thru-hull? Goes for OP too.....

Peter

 

[backinblue]

Shouldn't there be a vented loop between macerator and thru-hull? Goes for OP too.....

Peter

Maybe...but there isn't as far as I know. I'll take another look. I don't think it's needed because it could not flood the boat unless the tank is leaking. Worst case it fills the holding tank about 30%.

 

[rslifkin]

Shouldn't there be a vented loop between macerator and thru-hull? Goes for OP too.....

Peter

There probably should be, but my boat was built without one and also has the same back-filling problem. I think the vented loop is commonly skipped in this application as the seacock is not normally left open when the macerator is not in use. Plus the worst issue it'll typically cause is a holding tank full of seawater that needs to be pumped out.

 

[mvweebles]

Well, worst case is quite s bit worse than a partially full holding tank. Unlikely perhaps.

Because of caustic nature of sewage, these thru-hulls are prone to freezing in place. If it were to be left open and unable to be closed, would create a chronic filling and unable to repair without creating a mess or a haul.

Peter

 

[rslifkin]

Well, worst case is quite s bit worse than a partially full holding tank. Unlikely perhaps.

Because of caustic nature of sewage, these thru-hulls are prone to freezing in place. If it were to be left open and unable to be closed, would create a chronic filling and unable to repair without creating a mess or a haul.

Peter

True. But that risk of sticking open is all the more reason to open and close the valve every time you use it.

 

[mvweebles]

True. But that risk of sticking open is all the more reason to open and close the valve every time you use it.

Just between us kids, despite knowing the wisdom of routinely exercising them, have you never had a frozen thru-hull?

Peter

 

[rslifkin]

Just between us kids, despite knowing the wisdom of routinely exercising them, have you never had a frozen thru-hull?

Peter

I've had some get a bit sticky and need some TLC, but I've never had one freeze up entirely. But even if I never cycle any of mine for exercise, they get cycled at least twice a year when we winterize the boat, prep for spring launch, etc. And most get cycled a couple of times during the season to clean out intake strainers. The most at risk is the macerator discharge, but that's most likely to stick closed (as we boat in the Great Lakes, so it's kept ziptied shut unless it's cycled for exercise).

 

[C lectric]

Sounds like your vent line is clogged for this to happen in the first place. Your discharge thru hull should be closed when not in use, whick would prevent this as well but something is off with your vent line

I agree with Gdavid. Check the vent line. They can and do plug either from hose failure or critter [bugs] action.

 

[backinblue]

I agree with Gdavid. Check the vent line. They can and do plug either from hose failure or critter [bugs] action.

Or from overfilling your tank and forcing "stuff" into the vent hose.

 

[backinblue]

Shouldn't there be a vented loop between macerator and thru-hull? Goes for OP too.....

Peter

Peter, thinking about this for a minute more, would a vented loop help? I think not because it's not a siphon situation. If water is being pushed into the thru hull, would a vent make a difference?

 

[HeadMistress]

When a below-waterline thru-hull is left open, water outside the boat will use it to seek its own level INSIDE the boat, so water will rise in a tank to the boat's waterline. A macerator pump can slow this down, but cannot block it...which is why holding tank overboard discharge thru-hulls should always be kept closed except when in use.

Because humans are fallible and can sometimes forget to close a thru-hull, ABYC standards call for a vented loop in all lines connected to below waterline thru-hulls. However unlike building codes on land, compliance with standards is voluntary, so whether to install one depends on your risk tolerance.

Check the vent line. They can and do plug either from hose failure or critter [bugs] action

Regular preventive maintenance can, as the name implies, prevent vent blockages. Easy to do if you replace the vent thru-hull that's actually designed to keep sea water out of fuel and fresh water tanks with an open bulkhead (aka "mushroom") thru-hull...the kind you can stick your finger into. This not improves air exchange via the vent, but prevents vent blockages by allowing you to put a hose nozzle against it to back flush the vent line every time you pump out and/or wash the boat. Anything that's tried to set up housekeeping in it will just get a water slide ride into the tank.


--Peggie

 

[Comodave]

And most boat manufacturers don’t put an adequate size vent in to allow air flow into the tank. I added 2 1.5” vents, one to each side of the boat so air can flow through the tank. And with 1.5” vents it is unlikely they will get clogged up. Air in the tank will help aerobic bacteria to grow. When a holding tank has aerobic bacteria it doesn’t smell. When it has anerobic bacteria it will stink.

 

[MYTraveler]

As long as vent to tank is not clogged, should be fine.

Peter

Agreed, but if you are sucking in water with the discharge line open, your vent is probably clogged. In that case, high vacuum may damage something. In that regard, my holding tank pumps overboard through a diaphragm pump with duckbills at each end. sucking the pump backwards can cause the duckbills to invert or be otherwise damaged.

 

[grahamdouglass]

I have a filter in my vent line

I don't have a straight vent hose to the out side. I have a filter, about 18" long inline in the vent hose.

When I was pumping out, with the dock pump out facility, the flow of sea water was continuous.

A feature of the bellows pump is it allows a flow thru when suction is applied to the pump out hose. Both pump out and ocean discharge have a scoop at the bottom of the tank so the sea water would enter the holding tank via the scoop of the ocean discharge at the bottom of the tank and then be sucked up by the scoop of the pump out. Both scoops are within 1/2" of the bottom of the tank.

 

[HeadMistress]

1. The Dometic/SeaLand T- Series pump is not what anyone would consider "high vacuum"...it's a diaphragm pump. I've never seen one run backward unless it was set back into place backward after replacing the duckbills

2. The system would have to have two pumps in the overboard discharge plumbing--one to discharge tank contents and one to pull in sea water through an open discharge thru-hull., so sea water isn't being pulled it, it's just doing what water does: Seeking its own level INSIDE the boat via any open route...the vent doesn't enter into it. The discharge pump can only slow it down a bit.


--Peggie

 

[Comodave]

I don’t like filters in vent hoses. They inhibit air flow, which causes anerobic bacteria that really stinks. And they can get clogged and stop venting. Then with no effective venting when you pump out you could crush the holding tank. That you really don’t want to happen.

 

[grahamdouglass]

There is some confusion on my holding tank

My holding tank has ONE pump, it is a bellows pump that sits on top of the holding tank that only discharges to sea through a thru hull.
I know this is a bellows pump because I had to buy it and install it 2 summers ago when I replaced the original. I personally installed this holding tank, tank sensors and hoses when I bought the boat.

The only other pump involved, on the boat, is the hand pump that pumps the toilet contents to the holding tank.

The other pump I refer to is the Yachtclub pump-out pump. This is the large pump, in the pumphouse on the dock. It connects to a hose that goes to my deck outlet that pumps my holding tank contents to the city sewage system.

I have edited my previous post,#21, to clarify it.

I've been thinking about getting rid of the filter, I might try that.

 

[Bacchus]

That filter may be plugged.
I would eliminate it as a first step. Get your pumpiut working correctly and then assess tank smell and need. / best course of action to solve that, if needed.
Sometimes (my case ) adding an inexpensive DIY tank bubbler was easier than trying to fix my poor OEM vent. I have since found an alternate route for a new vent at the bow.

 

[Mac2]

I use an air compressor. Not sure if this is applicable to this post, but thought it was worth mentioning. My holding tank is several hundred gallons (steel). My vent hose is 1 1/2 inches, but has about 10 feet of head pressure. It was taking me forever to pump out. A commercial pump out specialist was waiting for me and suggested I use a compressor to positively pressurize the holding tank as I pump out. I already had air lines near the holding tank (from my old r/v toilets that used air to open the flapper to flush). I tapped the holding tank and put a gate type valve on the air line. When I pump out I open the valve (about 3/4 turn) until I hear the maximum flow through the line. A huge difference between closed-no air, and a slight amount of air.

 

[SteveK]

I've been thinking about getting rid of the filter, I might try that.

My previous boat had such a filter. When I overfilled the tank, the filter got wet and it was clogged, would not let air pass through. pump out was slow as I had to start/stop to let air in through discharge. No more filter and pump out was smooth.

 

[porman]

Just a random thought here. If the vent filter is plugged and the overboard discharge seacock is open, could the dockside pumpout have inverted the two duckbill valves in the T pump and allow sea water into the holding tank and then out through the deck fitting?

 

[GoldenDawn]

Your tank should be vented. If not, the vacuum could cause the tank to collapse. I did volunteer pump outs for a few years and I always asked the owners if they knew where their holding tank vent was and if it was clear. One owner I asked did not know, so we started tracing the vent line from the holding tank and found the open end in the linen closet - it had been disconnected during a refit and never reinstalled.

 

[porman]

Both of our holding tanks have a built in flap valve in the top to prevent the tank from imploding if the vent is plugged. Not boating related, but the Porsche 928's had plastic fuel tanks with a vent line that went into the right front fenderwell, behind a wheelwell liner. One of our customers lived on a dirt road that got real muddy in the winter and he plugged the vent. The fuel pump was strong enough to collapse the tank.