Black water tank pump-out

[afterwork]

Hi everyone. I have recently purchased a 2009 Jeanneau 50DS. I have a problem with a seized seacock which connects to the black water tank in one of the heads. As there are 2 other heads, this is not a big issue as I can use the other heads to wait until the next haul-out to replace the seacock. In the meantime, I do want to get the tank pumped out so it’s not holding stagnant black water for months.

My current marina offers pump out services but they are not used very often as I am in Southeast Asia and pump outs are not a regulated requirement so boats hardly use them. I have been talking to the marina supervisor and he has no experience using the pump out on a sailing yacht. He has expressed a concern that their pump has a 10 bar suction and could collapse my tank. He also says that the large yachts he uses it on have a “compressor” (I guess it should be a pump) that helps push out the black water from the tank. Based on this, he doesn’t think that the pump out would work on my boat (but again he doesn’t have experience doing it on a sailboat).

I have my doubts on his comments and I would think that the vent line would not allow the tank to collapse if properly vented. I could not find anything online for max pressure for suction on the tank.

Does anyone have experience with pumping out black water in marinas that usually serve larger yachts and have these high pressures? Anyone heard of issues with suction if there is no device to push the contents out? Any recommendations are welcome.

[markxengineerin]

A perfect vacuum is no gas at all, zero pressure. The atmospheric pressure at sea level is 1 bar, 760mm of mercury. So the difference between zero and one bar is 1 bar, max for a perfect vacuum.Oct 31, 2020

So 10 bar suction is not accurate. I don't know much about this, but I would not be afraid to try it MYSELF(!) with just the vacuum side, no attempt to pressurize anything. If you cautiously + slowly seal off the connection between the vacuum hose and your tank outlet, you will slowly create more and more vaccum. You don't need to create more than is needed to get the crap flowing. Use gloves and wear goggles, lots of rags, trash bags, etc.

[gonesail]

no overboard pumpout on the boat?

[afterwork]

The seized seacock is for gravity drain. No pump-out on the tanks.

[Jammer]

Depending on the setup, yes, you can screw up your tank if the vent line is plugged. 10 bar suction is just wrong but there's still a concern.


There are various ways to make sure the vent is doing its job. An experienced pumpout operator will listen for it to hiss then stop after pumping out the first few gallons.

[afterwork]

Originally Posted by Jammer

Depending on the setup, yes, you can screw up your tank if the vent line is plugged. 10 bar suction is just wrong but there's still a concern.


There are various ways to make sure the vent is doing its job. An experienced pumpout operator will listen for it to hiss then stop after pumping out the first few gallons.

Experienced pumpout operator is the main part I’m missing

[Flatswing]

Vent lines are usually 5/8” and notorious for plugging especially if a carbon odor filter is used. Is there an access port on the tank that can be removed to allow air ingress while pumping out or perhaps an intake hose at the top of the tank that can be temporarily removed?

[GordMay]

As others have noted, 10 bar suction seems implausible.
[10 bar ≈ 145 psi ≈ 295"Hg]

Most marine sewage pump systems can generate more discharge pressure, than vacuum, which means they can discharge greater distances, than they can suck.
Typical Marina Sewage Pumpout systems have a suction [vacuum] pressure of around 15"Hg [±0.5 bar, or 7.4 psi], up to 30"Hg [1 bar ≈ 15 psi].

[Jammer]

Originally Posted by GordMay

As others have noted, 10 bar suction seems implausible.
[10 bar ≈ 145 psi ≈ 295"Hg]

Quite; it is also at odds with the laws of physics. 1 bar is the theoretical limit (with small adjustments for weather and altitude).

[SailFastTri]

Originally Posted by markxengineerin

So 10 bar suction is not accurate. I don't know much about this, but I would not be afraid to try it MYSELF(!) with just the vacuum side, no attempt to pressurize anything. If you cautiously + slowly seal off the connection between the vacuum hose and your tank outlet, you will slowly create more and more vaccum. You don't need to create more than is needed to get the crap flowing. Use gloves and wear goggles, lots of rags, trash bags, etc.

This is horrible advice - it is VERY likely that the OP will get a literal sh#t-shower if he tries that method. Been there, got the medal
When pumping out you MUST have a tight seal of the pumpout hose to the deck fitting port. The hose should be equipped with a shut-off valve at the connection point to the deck fitting.
1 - Close the valve to the pumpout hose and turn on the pump.
2 - Attach the pumpout hose to the deck fitting (or push it firmly against it if equipped with a rubber interface)
3 - slowly open the valve. You should feel (and hear) the sewage flowing out. If so, open it all the way until the flow subsides.
4 - WHILE STILL FIRMLY ATTACHED TO THE DECK FITTING close the valve. You can open it again a few times to get more out.
5 - The valve must be closed to remove the hose without worry of splash back. Just in case there’s any residual suction you should break the seal slowly by angling the suction hose.
You can rinse and repeat.
PS - Just don’t be that guy who inserts the same garden hose used by other people to fill fresh water tanks. Sorry for adding this - I’ve seen it done