Holding Tank Pumpout Not Fully Evacuating

[Sailmonkey]

Originally Posted by S/V Adeline

Why would the bottom mounted fitting be less ideal? Possible leakage?

Any leaks/cracks/breaks....etc are free to dump out unhindered.

Although we’ve got our tank plumbed this way for gravity drain.

[lordgeoff]

Originally Posted by Stasis

I have recently acquired a boat with a 40 gallon holding tank. When doing a pumpout (liveaboard marina) it leaves about 2 inches in the bottom of the tank. This results in the worst and smelliest of the waste settling to the bottom and never being pumped out. Is this typical? Is there any modification I can do to get it to pump out the tank fully?

Refill it with salt water and dump it using gravity if it is bothering you.

[Gerrycooper56]

Do you have an electric macerating head?

[jlcarreiro]

I also use the sink water not salt water. I keep a milk jug filled next to the toilet. We also request men sit down to pee, no spraying!

[rwaldrop13]

One of our liveaboard neighbors keeps spray bottles of white vinegar next to each toilet. After flushing wait a few seconds and spray bowl down thoroughly. Next time it flushes vinegar goes thru lines and helps keep odor and buildup down. They have done this now on 3 boats amd swear by this methodology.

[peghall]

Originally Posted by jlcarreiro

I also use the sink water not salt water. I keep a milk jug filled next to the toilet. We also request men sit down to pee, no spraying!

An easier way to flush using sink water: Sink drain thru-hulls are below the waterline on almost all sailboats. So re-route the toilet intake hose to tee or wye it into the sink drain line as close to the seacock as possible because the connection must be below waterline to work unless you're sure you'll never want to flush using sea water.
This will allow you to flush normally with sea water. After you’ve closed the sink drain seacock in preparation to close up the boat (you do close all seacocks before leaving the boat to sit??), fill the sink with clean fresh water and flush the toilet. Because the seacock is closed, the toilet will draw the water out of the sink, rinsing the sea water out of the entire system—intake line, pump, channel in the rim of the bowl and the discharge line,(Water poured into the bowl only rinses out the toilet discharge line). If your toilet is electric, be careful not to let it run dry…doing so can burn out the intake impeller. Or you can keep the sink drain seacock closed except when it's needed to drain the sink and flush with fresh water down the sink all the time...your choice.


--Peggie

[dfelsent]

We’ve been fresh water flushing for the first time this year. A game changer.
Both heads have showers on hand held hoses. Perfect for flushing!
We do use salt water during pump outs for tank rinsing. That little bit does not seem to hurt.

[RamNemesis]

Originally Posted by Shrew

RE: "add a little water" It's not an issue with solids, the entire contents are (or should be liquid).

Once the vacuum starts sucking air, it won't get the rest. If the pickup tube is on the side or the top, the gap from the bottom to the top of the side mounted fitting, or the gap from the pickup tube to the bottom will never be able to be sucked.

Your best bet would be a bottom mounted fitting.

Once the level gets low a vortex forms causing air to get in and then give the illusion of an empty tank.
Some options are
install output under the tank,
Angle the tank so it leans more the outlet pipe.
Make a wider nozzle to reduce the vortex's (vortii??) forming.

Another options is to install an aerator like in fish tank. this promotes a break down of the waste rather than letting it rot and smell. Think of it as composting almost. You will still have 2 inches at the bottom but at least it wont smell as bad.