Is odorless really odorless?

[Bigjim]

Originally Posted by peghall

However tank shape is actually the LEAST of what's wrong with OEM tank installations...boat builders are--hands down--the WORST sanitation system designers and plumbers on the planet! They're guided entirely by the lowest possible cost way to do it. I've seen enough nightmare OEM systems to write another book on that alone!

--Peggie

Shape may not be the most important aspect, but as a former tank truck driver, I can say that tank shape is important if you want it to empty properly. Most of the standard tanks designs are all rectangular. My tank truck was basically a horizontal cylinder so all liquids would pool at the lowest point and could drain properly.

Designers rarely have to work on or repair their designs so designing any system is a abstract concept to most of them. Look at the standard electrical systems of boats and you can see that they never considered the owner 10 years down the road.

[David B]

Originally Posted by Bigjim

I think one of the problems with boat plumbing is the design of the tank itself. Why are they rectangular? They should have a "v" bottom to funnel all the goop to the lowest spot. It's impossible to pump out a rectangular tank completely. There will always be residue left behind.

Some do - ours does. Also the pump out pipe goes to the bottom of that sump area, plus there is a gravity drain there for when at sea. Works very well. The brand is Bomar from memory - as used by Beneteau etc

[David B]

Originally Posted by peghall

Although it's rare to find an off-the-shelf tank in a retail marine store or catalog that isn't rectangular, there are several tank mfrs who make non-rectangular tanks. Ronco Plastics is the best known. Not only do they make TOP quality thick-walled (at least 3/8") water and waste tanks for a very reasonable price, they have more than 400 shapes and sizes, over 100 of which are NON-rectangular, and they install fittings in the sizes and locations specified by the customer when they make the tank. There are retailers who sell Ronco tanks, but Ronco sells direct for a much lower price...and they're great to work with. Their current marine catalog is here Ronco Plastics marine Tanks And because so many people told 'em their previous catalog is much easier to search, you'll find that one here Ronco Plastics old marine catalog.

Other mfrs who also offer rotomolded polyethelene non-rectangular tanks are Moeller Marine Trionic Corp tanks Moeller Marine and DURAWELD

It's important to check things like their wall thickness, availability of custom fittings locations and sizes and upcharges for them as well as for increased wall thickness.

In the unlikely event you can't find a size and shape that works for you among all those mfrs, Triple M Plastics Triple M Plastic Products Inc makes top quality custom molded plastic tanks.

However tank shape is actually the LEAST of what's wrong with OEM tank installations...boat builders are--hands down--the WORST sanitation system designers anplumbers on the planet! They're guided entirely by the lowest possible cost way to do it. I've seen enough nightmare OEM systems to write another book on that alone!

--Peggie

Vetus do some nice tanks too, with nice mounting lugs and nice fittings. Many shapes.

[peghall]

Vetus do some nice tanks too, with nice mounting lugs and nice fittings. Many shapes.


And they're fine for water and in some cases, fuel...but I'm not a fan of flexible tanks (bladders) for sewage holding for several reasons. 1. Sewage generates gasses which, if the vent line becomes blocked (it's illegal to use an unvented bladder for sewage holding) can pressurize the tank and blow out fittings. 2. They're often just stuffed into an available space without doing what's necessary to protect them from chafing, often all the way through. The best quality bladders resist it a lot longer than the cheapest ones, but neither is immune...3. A decent quality bladder typically has a lot higher price tag than a comparable top quality rigid plastic tank..and 4. Even the best bladder has only about a 15 year average lifespan...a top quality rigid plastic tank will have as long a lifespan as the boat as long as it's not abused (over-tightened fittings, seriously pressurized as a result of of a blocked vent).


--Peggie

[David B]

Originally Posted by peghall

Vetus do some nice tanks too, with nice mounting lugs and nice fittings. Many shapes.


And they're fine for water and in some cases, fuel...but I'm not a fan of flexible tanks (bladders) for sewage holding for several reasons. 1. Sewage generates gasses which, if the vent line becomes blocked (it's illegal to use an unvented bladder for sewage holding) can pressurize the tank and blow out fittings. 2. They're often just stuffed into an available space without doing what's necessary to protect them from chafing, often all the way through. The best quality bladders resist it a lot longer than the cheapest ones, but neither is immune...3. A decent quality bladder typically has a lot higher price tag than a comparable top quality rigid plastic tank..and 4. Even the best bladder has only about a 15 year average lifespan...a top quality rigid plastic tank will have as long a lifespan as the boat as long as it's not abused (over-tightened fittings, seriously pressurized as a result of of a blocked vent).


--Peggie

Totally agree Peg - actually I don't trust flexible tanks for anything. No Vetus do (or someone does it for them) rigid ones too. Very solid, and some are specifically listed for grey/black water holding, with a drain sump at the bottom, suction pipe etc, and some very nice hose fittings with decent flanges and 'O'-ring seals etc.

Here is one example similar to one I used for greywater.

https://www.vetus.com/en/waste-water...ted-waste.html

[peghall]

Vetus rigid tanks do look impressive...but I didn't see any that aren't rectangular. All the mfrs I listed also offer non-rectangular tanks

--Peggie

[Bigjim]

Originally Posted by David B

Vetus do some nice tanks too, with nice mounting lugs and nice fittings. Many shapes.

I stumbled onto Triple-M a couple of years ago. I was going to have them build new water tanks for me. Mine are 40 years old and had cracks in them when I bought the boat. I sealed up the cracks but I think one of them is leaking again.

The big issue with my water tanks is the pick up tube. It did not go all the way to the bottom so I have to modify them. If I get new tanks that will be the main redesign point: setting up better "pick up tubes".

Which brings up another question: I've seen that some holding tanks have "pick-up" tubes instead of drain fittings. The advantages of a pick-up is that you can design a sump for the lowest point of the tank and pick up the waste from there and waste cannot sit in any part of hose at any time, however, a pick-up can never get everything out of the tank and could be a point for clogging. Does anyone have any experience with such a tank design?

My tank has a drain at the bottom of the tank so, if the tank is getting full, some of the waste will be held in the pump-out hose. Is there any alternative to this situation without using a pick-up tube? I can angle the hose upward a bit, but there will alway be part of the hose that will have waste in it.

Would it be a good idea to swap out the hose barb for a hard PVC elbow connector or standpipe? I'm worried that the PVC would not stand up to the deflection force from the hose without some sort of framework or armature.

[thinwater]

Originally Posted by Bigjim

I stumbled onto Triple-M a couple of years ago. I was going to have them build new water tanks for me. Mine are 40 years old and had cracks in them when I bought the boat. I sealed up the cracks but I think one of them is leaking again.

The big issue with my water tanks is the pick up tube. It did not go all the way to the bottom so I have to modify them. If I get new tanks that will be the main redesign point: setting up better "pick up tubes".

Which brings up another question: I've seen that some holding tanks have "pick-up" tubes instead of drain fittings. The advantages of a pick-up is that you can design a sump for the lowest point of the tank and pick up the waste from there and waste cannot sit in any part of hose at any time, however, a pick-up can never get everything out of the tank and could be a point for clogging. Does anyone have any experience with such a tank design?

My tank has a drain at the bottom of the tank so, if the tank is getting full, some of the waste will be held in the pump-out hose. Is there any alternative to this situation without using a pick-up tube? I can angle the hose upward a bit, but there will alway be part of the hose that will have waste in it.

Would it be a good idea to swap out the hose barb for a hard PVC elbow connector or standpipe? I'm worried that the PVC would not stand up to the deflection force from the hose without some sort of framework or armature.

As a refinery guy, I've dealt with everything. And I've had pick-up tubes in waste tasks.



No, never had one clog. However...


With chemical tanks, such as acid, would you rather have to pull a pick-up tube and cleaning it out or pull the hose off and open the valve on a full tank of acid? The nice thing about pick-up tubes is that if they clog they are easy to pull without mess.


The practical extent to which they MT the tanks is usually the same. With sludge and junk, unless there is a steep slope you are going to leave 1-2 inches anyway you look at it. And it doesn't matter. Some folks obsess over MTing the tank every time they come in, and then flush it, as though that will make it smell less. Logically, not true unless actually cleaned.The same vapors are there either way.


The advantage of bottom drain is gravity drop is possible (but only if the tank is high, which is a different problem) and a shorter draw to the pump. Disadvantages are another valve, another fitting that can crack, harder to unclog, and longer hose runs in deck pump-out systems.


You see a lot of dip tubes in chemical plants in tanks that are relatively small (less than 5000 gallons) or that contain hazardous chemicals.

[David B]

Originally Posted by peghall

Vetus rigid tanks do look impressive...but I didn't see any that aren't rectangular. All the mfrs I listed also offer non-rectangular tanks

--Peggie

True, but they have a sump down the bottom of the ones designed for waste, so it all drains well.