Gravity Holding Tank Installation Questions

[silverp40]

The hose is 1 1/2" Sealand Odor plus. We have been happy with this hose type over the last 5 years or so.

The valve is a marelon 1 1/2", no handle because it does not fit.

I would not recommend a marelon valve because of it's shorter life span. A Groco ball valve would do better over time.

[Cheechako]

I found with my gravity feed tank that if you are moving often the waste macerates it self into slurry and easily discharges. I had an exit hose about 4 ft long. At the seacock installed a bronze Tee going to the pump out. With the seacock closed and locked you're in legal mode. with the seacock open it just goes right out.

[Roy M]

My gravity feed works like a dream. The LAVAC pump completely pulverizes everything. Even the TP gets completely destroyed, as evidenced when I open the big grey industrial ball valve in open water. A sudden rush and a great brown cloud, then I pump some fresh seawater to flush the tank out, close the valve and add a fresh shot of K.O. aerobic bacteria. And not burning out the motor of a macerator....priceless!

[silverp40]

Roy, the picture looks like there is a diaphragm pump on the outlet side of the tank....Do you have it installed so that you can pump it out manually overboard also?

Regards
Ovi

[ccannan]

Roy,

Thanks for sharing the photo. Please provide more details about your head/holding tank plumbing. As silverp40 suggested, it looks like there is a diaphragm pump downstream of your holding tank and "big greyindustrial ball valve". Thanks.

[ccannan]

silverp40,

Thanks for sharing your photo.

What are the rough exterior dimensions of your holding tank, and approximate usable capacity?

Is the fitting that is visible in the top left corner of the tank, the vent line?

Are you suggesting that your Marelon ball valve is wearing out after 5 years?

What are the 120 degree elbow and y connection made from? PVC? Are they also 5 years old? How are they holding up?

[Roy M]

My tank is about 25 gallons capacity. It is built with 1/2 " birch plywood (Baltic Ply) with epoxy seal. Two vents, at the top using 90 degree elbows, exit port and starboard sides of the bow, with 1 1/2" hose, per Peggy Hall's guidance. At the bottom is a simple throughhull fitting leading to an 1 1/2" waste hose to a tee fitting. The tee leads to a deck cleanout port. and downhill to the ball valve, a 90 degree ell and a discharge about 6 inches above the waterline. The sole pump is a Whale 10 (instead of the supplied Henderson for the Lavac), which evacuates the toilet bowl. pumps out upwards to the top of the holding tank. The two vents, at the top of the tank, cross over and vent port and starboard at the the bow, providing profuse ventilation for the aerobic bacteria in the holding tank. The only pump is upstream of the top of the tank. Gravity, alone, is the sole mover of waste over the side.

The black electric pump is a high capacity, high pressure saltwater washdown pump to clean the anchor and deck, and to squirt passing boats with a 30-40 stream of seawater.

[silverp40]

Chip

The tank is approx 17"X36" and I calculated it holds about 14 gals .

The top fitting is an airvent that vents under the toerail. The 45 elbow is PVC as are the other fittings connected to it that lead to the discharge hose.

The marelon valve is only a few months old and works perfectly - however, upon speaking to the Groco R&D guys, they advised me that the marelon valves have a relatively short life span and get harder to operate after a year or two. Lubricating them every year is helpful (according to Forespar) but it is a NOT easy to do once it's installed...

Hence, the Groco Bronze IBV valve with the chromed 316 ss ball was suggested as having the longest life span in this harsh environment...this is from someone who designs and researches valves for marine plumbing.

Hope this helps.

[rossny]

Hi All, I am refitting existing direct overboard manual heads with small vertical holding tanks. I have ordered marine tanks with two 1 1/2"FPT and one 1"FPT on top and one 1 1/2"FPT on the bottom. On top the first 1 1/2"FPT will be a 90 deg plastic barb fitting to attach hose from head, second 1 1/2"FPT is strait plastic barb to short hose to deck pump-out above and 1" is for plastic barb to vent hose to 1" 90 deg plastic thru hull as vent outlet. The bottom 1 1/2"FPT is for a nipple to 1 1/2" plastic ball valve with plastic barb to hose going to sea-cock below. The heads use fresh NOT seawater to flush.
Questions A: I can not locate purpose made vent fitting in 1", will the thru hull take in lots of water to fill my small tank every hard rain? B:do I add a pick up tube in the pump-out fitting, should it be glued to the fitting or the tank, how close to the bottom of the tank should it terminate, is a 45 deg cut at the bottom of the tube the best angle? C: to be legal I need to lock the ball valve, can I just drill a hole in the handle for a padlock and rig a locking hasp or does it need to be an official HEADLOCK. D: am I intellectualizing this too much...should I have my head examined?
Thank you!

[peghall]

A: I can not locate purpose made vent fitting in 1", will the thru hull take in lots of water to fill my small tank every hard rain?

So-called "vent" thru-hulls are only available in 5/8"...use a common bulkhead fitting for the 1". If you're concerned about taking on water through the tank vent, put a clam shell cover over it.

B:do I add a pick up tube in the pump-out fitting, should it be glued to the fitting or the tank,

If the pumpout fitting is at the top of the tank, a pickup tube is necessary. Use PVC pipe...glue it to the fitting.

how close to the bottom of the tank should it terminate, is a 45 deg cut at the bottom of the tube the best angle?

It should just touch the bottom of the tank, cut at about 25 degree angle. That will leave only about 1/2" in the tank.

C: to be legal I need to lock the ball valve, can I just drill a hole in the handle for a padlock and rig a locking hasp or does it need to be an official HEADLOCK.

I don't even know what a "headlock" is except as a wrestling hold. All you need to be "legal" is a hole in the handle big enough to run a locking tie wrap through and something else to secure the tie wrap to.

D: am I intellectualizing this too much...should I have my head examined?

They're good questions...it's always better to ask '"what should I do" than "What should I have done?"

[Cheechako]

Originally Posted by rossny

Hi All, I am refitting existing direct overboard manual heads with small vertical holding tanks. I have ordered marine tanks with two 1 1/2"FPT and one 1"FPT on top and one 1 1/2"FPT on the bottom. On top the first 1 1/2"FPT will be a 90 deg plastic barb fitting to attach hose from head, second 1 1/2"FPT is strait plastic barb to short hose to deck pump-out above and 1" is for plastic barb to vent hose to 1" 90 deg plastic thru hull as vent outlet. The bottom 1 1/2"FPT is for a nipple to 1 1/2" plastic ball valve with plastic barb to hose going to sea-cock below. The heads use fresh NOT seawater to flush.
Questions A: I can not locate purpose made vent fitting in 1", will the thru hull take in lots of water to fill my small tank every hard rain? B:do I add a pick up tube in the pump-out fitting, should it be glued to the fitting or the tank, how close to the bottom of the tank should it terminate, is a 45 deg cut at the bottom of the tube the best angle? C: to be legal I need to lock the ball valve, can I just drill a hole in the handle for a padlock and rig a locking hasp or does it need to be an official HEADLOCK. D: am I intellectualizing this too much...should I have my head examined?
Thank you!

just put the pump out on the bottom. or tee into the bottom if you already ordered the tank. use a std 5/8 vent fitting and hose. you may be overthinking this.

[peghall]

He's not overthinking it at all. The larger vent will help to keep the tank aerobic, which prevents odor out the vent and a pumpout fitting on the top of the tank, with a pickup tube INside the tank prevents one hose from permeating and stinking.

[RHoodJr]

On all of your recommendations I have accumulated all the parts necessary for a tank installation. I bought a Ronco tank that measures 5” depth, 15” high 32” wide and plan to install this on the bulkhead behind and above the head. I will be using 1 1/2” schedule 40 PVC with Sealand semi flexible hoses to connect to the head and thru hull. I will also be using 1” hose and thru hull for venting.

I was planning on building a shelf and inverted “L” shaped ends of marine 3/4” plywood that has been fully coated with West System epoxy, to secure the tank to the bulkhead. The tank has a capacity of 9 US gallons so I know the approximate weight when full.

That being said, can anyone comment on the proposed installation? Can anyone give me an idea of the load forces of this tank and it’s contents in a seaway? The shelf and side brackets will all be thru bolted to the bulkhead. Any ideas/criticisms would be helpful.

Thanks

[jr_spyder]

I have a very similar project going on but with a 21 gal tank. By my math when full it will weigh about the same as me. So my test is if my shelf/brackets can hold my weight, including replicating being in a pounding sea. Not very scientific, but close enough, and it promises to be amusing to do the testing.

Good luck,

JR

[Pblais]

You can figure 8 pounds (US) to the gallon (US) as a rule of thumb. Water weighs that and poop weight less than water by volume though it is mostly water. To me 9 gallons is not that much. 20 seems to me to be minimal yet adequate. 9 gallons might last my wife most of a weekend. All the proposed plumbing sounds fine though.