Critique my holding tank system design please

[elaak]

Hi there, writing to the brain trust to help me critique my new replacement holding tank system design. Replacing an electro scan with an entirely new system.

Goals:
- no electric motors
- gravity drain
- ultra short pathway for direct overboard mode

Concerns:
- head lift height. Is 1m of lift okay?
- back flow in bowl. Is this an issue if the joker valve is in good condition?
- is a 300cm hose run okay for the discharge to the holding tank?
- will solids settle in the long low spot in the pipe?
- is the 15cm difference in height between the holding tank bottom and discharge vented loop enough for gravity to work it’s magic well enough?

Cheers friends and thank you for the hard earned wisdom

[sailingabe41ds]

Hi..
Aren't you going to have poop sitting in that 150-200cm pipe? I would hope that the gravity drain from the holding tank is on a decline all the way to the outlet. The same when leaving the head...everything should be on slope. That said, I am not a poop expert.
Abe

[Frankly]

To have a holding tank above the bowl lip is putting a lot of faith in things never weeping or actual failing.

15 years back I decided on an not novel but a little out of the mainstream configuration. Short length of sch 40 PVC/ hose directly to top of tank (top of tank approx 1/3 bowl height). Y valve on tank discharge. One feed deck discharge, other maceration pump overboard. Other than a couple of maceration pumps and new joker valve every two years the system has operated trouble free.

Advantage as I see: head pumping against almost no hyd head, No vented loops (vent on tank). 2" (sink your yacht in a hurry) discharge valve normally closed except macerating. Short line/ pipe head to tank (no odor). Toilet always directed to tank.

One other little benifit is that coming in from offshore or dockside if not offshore empty tank. Squirt a little simple green in bowl, fill couple of times fresh water, pump into tank and let it slosh on the way home. Near home pump tank dry and fill with simple green and single bowl fresh water. That is way stored dockside (sloshes around). Everything clean and 18YO aluminum holding tank still holding.


Frankly

[mvweebles]

Pickup Peggie Halls book on Amazon. "Curing boat odors" or something like that. She strongly recommends keeping sewage lines as short, low, and as straight as possible. Sort of the opposite of what you have designed.

Pumping effluent through 3-meters of 1.5 inch hose with a manual head is a tall order. Lifting it a meter is yet another matter. Expecting a joker valve to retain the hydrostatic pressure might work for a while.

My sense is this is the type of design that works better on paper than reality - lot of machinations just to avoid a maceration pump. But who knows? What's the worst that can happen?

Good luck

Peter

[Dockhead]

Originally Posted by mvweebles

. . . - lot of machinations just to avoid a maceration pump.. .

In my opinion you definitely want the tank below the toilet and with the shortest, straightest hose possible with a positive slope the whole way, if at all possible.



That is really worth using an electric pump (or manual diaphragm pump if you prefer) to pump out the tank.

Joker valves never seal perfectly. Everything in that long line is going to flow back into toilet. The quality and condition of the joker valve will only determine how long it takes for that to happen.


Also, you really want a separate through hull for pumping the tank out. Can you even imagine what will happen if you open the gravity dump valve with the Y-valve in the wrong position? It doesn't even bear thinking about.


One other factor to keep in mind when thinking about hoses to the holding tank -- are you flushing with sea water or fresh? If you flush with sea water, you want to flush enough to clear the lines. Any urine standing with sea water in the hoses will calcify and cause problems. Another reason to make them as short as possible and without any place where waste can stand. Alternatively, a good reason to flush with fresh water.

Last criticism -- Jabsco manual toilet? In my opinion based on experience -- one of the worst manual toilets made. The Raritan ones with the levered cylinder are far better, but there are still better ones than that.

And why wouldn't you consider an electric, macerating toilet? These have a long list of advantages over manual ones. One of the biggest is reduced clogging because the waste is macerated at its source.

[fourlyons]

Have to agree with the others, this design breaks a number of basic rules. Basically, just as Frankly said, you can put the tank above the bowl, just put the through hull and pumpout deck fitting on the discharge from the tank with a valve to discharge overboard. Basically waste passes through the tank first, then gets dumped or pumped.
Had this on my boat for ten years and it worked fine, but the salt water and calcium issue is a real problem. You should plan on changing the hose on a regular basis.
I bought a marine bowl, no built in pump, then the large diaphragm pump that is used with the Lavac head, to evacuate the bowl. I would have just bought the Lavac head but don't like the tiny bowls.

[malbert73]

Most new boats plumb holding tank above head for gravity drain so that should work. I wouldn’t use a Y valve on toilet if you have gravity drain tank. Eliminate the vented loop, plumb straight to holding tank from head. In port the tank is closed, offshore just leave it open and waste will drain through. Much easier.

[goboatingnow]

I rebuilt mine. 800mm lift to top of holding tank , total pipe run 1.25m. Gravity discharge

No syphon breaks needed

8 pumps of air are needed after every flush to clear the pipe into the tank. Otherwise it seeps past the joker.

The OP system is totally over complicated imho.

Jabsco manual. Yes it’s terrible but I’ve three complete assemblies as spares !!!

[Sailmonkey]

We had a gravity tank for the last 12 years. Toilet up 2 feet into the top of the vented tank (pump dry to clear the line). No vented loop needed. Bottom of the tank has a valve to a short hose to the seacock. Open the seacock and let er rip. If direct overboard is desired, leave the valves open and the tank becomes just a wide spot in the hose.

[mvweebles]

Originally Posted by Sailmonkey

We had a gravity tank for the last 12 years. Toilet up 2 feet into the top of the vented tank (pump dry to clear the line). No vented loop needed. Bottom of the tank has a valve to a short hose to the seacock. Open the seacock and let er rip. If direct overboard is desired, leave the valves open and the tank becomes just a wide spot in the hose.

This means the entire holding tank is above waterline, no? Otherwise the tank would fill with sea water when the valve is opend. I'm having a hard time imagining a boat with room to mount a tank up that high (or how it would be secured, etc.). Not a criticism, just trying to wrap my head around it.

Peter

[fourlyons]

Originally Posted by mvweebles

This means the entire holding tank is above waterline, no? Otherwise the tank would fill with sea water when the valve is opend. I'm having a hard time imagining a boat with room to mount a tank up that high (or how it would be secured, etc.). Not a criticism, just trying to wrap my head around it.



Peter

It depends on the characteristics of the design. It might be a little difficult on an older, heavier, slack bilged boat which will sit deeper in the water. But any boat of moderate to light weight with the harder bilges common now sits higher in the water, putting the waterline fairly low in the boat.

[sail sfbay]

Holding tank above the toilet will not work UNLESS you install a lift pump on the toilet outlet to a high point above the holding tank with gravity flow from the high point to the holding tank.

[Cheechako]

Pump the poop from the toilet into the top of the tank.
Do not intersect it with the Tee on the bottom.
Have it drain direct to a thru hull close by.
You could eliminate the overboard discharge you show from the toilet and pump, send everything through the tank, even if you then drain it to the sea. (Assuming you know your gravity is going to work, mine did) KISS

[Cheechako]

Originally Posted by sail sfbay

Holding tank above the toilet will not work UNLESS you install a lift pump on the toilet outlet to a high point above the holding tank with gravity flow from the high point to the holding tank.

Mine worked fine. You dont think a toilet will pump to the top of the tank?

[Sailmonkey]

Originally Posted by sail sfbay

Holding tank above the toilet will not work UNLESS you install a lift pump on the toilet outlet to a high point above the holding tank with gravity flow from the high point to the holding tank.

Works fine for me.