Holding Tanks

[SloopJonB]

Is there any consensus on the best material for holding tanks?

I'm going to be installing a head system in a boat that has never had more than a bucket and I'd like to make the tank a gravity drain.

Is foam core glass/epoxy good or is metal better for this? If metal, alu or S/S?

 

[Fah Kiew Tu]

Is there any consensus on the best material for holding tanks?

I'm going to be installing a head system in a boat that has never had more than a bucket and I'd like to make the tank a gravity drain.

Is foam core glass/epoxy good or is metal better for this? If metal, alu or S/S?

Mine is welded grey PVC. So far no problems, no smells etc.

Gravity drains via a ball valve which is lined up with the deck pump out fitting so you can rod it if there's a blockage.

FKT

 

[yoyo]

Polyethylene is a good choice. Ronco has been around a very long time and have a myriad of sizes and can do custom. https://ronco-plastics.com

I didn't have space for it but did seriously consider this one for a gravity drain setup by Vetus.

 

[gptyk]

2nd polyethylene. Just buy one and install it.

All metals will not last.

 

[Foolish]

I would strongly recommend that you look into composting toilets. Everyone raves about them. I know a fellow who even removed his entire old head system (holding tanks and all) and installed a composting toilet. He is VERY happy with his decision. There is a lot of dicussion and videos on this and I have never heard a bad word. But heads and holding tanks on boats are a constant source of anger.

 

[steele]

I had an odd shaped space to install mine so I built one with plywood, epoxy, and fiberglass tape to reinforce the corners. This place was a big help, they had all the fittings etc, https://marinesan.com. I decided to not have a gravity drain since I did not trust my skills enough to guarantee a leak free set up. Having all the fittings on top of the tank greatly reduces the risk of a smelly disaster.

 

[Hitchhiker]

For a holding tank waste system, molded Polyethylene is the only sensible way to go.

 

[longy]

There is a company ( MMM?) that makes plastic tanks to any shape you want. Uses plastic seam welding to glue flat panels together. I've used them once, was happy with the product. They use a thicker sheet than the rotomold tanks have.
I've also used Ronco when they had a shape I needed, also good

 

[Zonker]

Barr plastics locally. Polyethylene https://www.barrplastics.com/box-shaped-plastic-tanks.html#.YyySJHbMJPY

BUT be sure to use a 2" seacock for the drain. Very important to get it to drain easily (learned this from Beneteau factory). RV dump valves are 3" and they empty very easily.

I have also ordered from Ronco; satisifed with the "we'll put the custom fittings where ever you want, just send a drawing"

I'd say in descending order of preference:

- polyethylene off the shelf
- polyethylene custom seam welded
- solid fiberglass (lay up 4mm thick flat sheets that are mat/resin rich, cut into shape, tape at seams)
OR build a MALE plug from melamine coated particle board with rounded edges. The tank will have 5 smooth faces laid over the mold, then an external flange for a flat lid. It is very very hard to make a home made tank totally waterproof on your first attempt.
- stainless

Not keen on foam/glass unless you are really confident in your ability to keep the foam dry 100%.

Never aluminum. The piss corrodes it very fast. I suppose you could coat it on the inside with an expensive epoxy coating.

 

[lakeneuch]

I have one of the Vetus gravity drain models mentioned earlier. It works and I haven't had any problems with it in two years. The finish of the tank is good and the installation of the hose fittings staight forward. I remember that when I wanted to install it one fitting that I needed was not in the "kit", but this was an oversight on my part, it was not listed as beeing part of the kit (but obviously now I don't remember what one it was...).
I have no smell problems, but I installed a charcoal filtered aeration for it.

 

[SloopJonB]

It looks like polyethylene is the consensus. I'll have to have one built though to fit the area I want it.

It has to go here leaving access to all those fasteners and with the head inboard of it. Luckily it's not a cruising boat so a big capacity is not a requirement.

Looks like a 3D cardboard template and a trip to the outfit Zonk named is in my future.

 

[Fah Kiew Tu]

It looks like polyethylene is the consensus. I'll have to have one built though to fit the area I want it.

It has to go here leaving access to all those fasteners and with the head inboard of it. Luckily it's not a cruising boat so a big capacity is not a requirement.

Looks like a 3D cardboard template and a trip to the outfit Zonk named is in my future.

View attachment 542466

Cardboard works, or thin doorskin ply hot glued together.

Second the requirement for a big dump valve, mine is 50mm and attached via a bolted flange on the hull side with a union on the tank side to eliminate those annoying 'clocking' issues where things don't quite do up tightly enough with the alignment you need.

FKT

 

[Well-known member]

I'd like to make the tank a gravity drain

I'm not an expert on things that run downhill. How will this system be evacuated of excreta? Does the "honey wagon" man come by and empty the contents in a bucket, drag it out to his cart and haul it away to use as "night soil"?

Asking for a friend.

 

[gptyk]

Bottom of tank is above the waterline. Open valve, gravity sucks the shit out.

I've got one on the current boat and it's far superior than a macerator tor for self-dumping.

 

[SloopJonB]

I'm not an expert on things that run downhill. How will this system be evacuated of excreta? Does the "honey wagon" man come by and empty the contents in a bucket, drag it out to his cart and haul it away to use as "night soil"?

Asking for a friend.

I'm assuming that was intentionally not in purple font - a gravity drain holding tank does just that - it's mounted above the waterline and can be drained by simply opening a valve on the bottom of the tank which is connected to a through hull - no pumping required.

 

[Son of Hans]

No one has mentioned bladder tanks yet. My Alerion came with one (I forget the brand) and I have no complaints. Bladders are widely used for fuel and other nasty stuff, so the technology is there. They probably don't make maximal use of the space available, but it is easy to see when you need a pumpout with just a glance. The fittings may not be best positioned for gravity drainage, but customization is possible.

 

[Well-known member]

Gravity requires a vacuum in my neck of the woods - hence the confusion (and the levity).

Habemus sentinis quod omnes cacat.

 

[Zonker]

If you can buy a Ronco off the shelf one it will be MUCH cheaper than a custom one however. Smallest is about 6 gals

Here's the 85 page catalog.

https://ronco-plastics.com/wp-content/uploads/2020/07/Marine2020-updated-7.3.2020.pdf

Unfortunately you have to go page by page and they are NOT in logical order of shape or size. I think any time somebody orders a custom tank, they just add it as another line in the catalog!

For example:

Vertical tanks are better than horizontal tanks. Can you do one sort of like a backrest

 

[ryley]

I prefer top-tank entry and dip-tubes for evacuation so 'stuff' doesn't sit in the connecting hoses. It also makes it less messy if you have to disconnect hoses and move tanks around.

 

[yoyo]

Simple Y-valve on the tank drain. One path to gravity drain, one to tank pump out sucker. Empties the entire tank and hose.