Confused about pipe sizes - trying to make dip tube for new tank

[Fredct]

I have read "the book" and I am ready to replace tank and all hoses. There is a nice post on the site for the same boat so i am nearly set.

I have ordered a tank with 3 female NPT fittings on top, 2X 1.5" for the business in and out and 1X 1" for the vent. So far, so good.

For the tank inlet, I am using a male threaded elbow (1.5" NPT) with barbed end. Same for the tank vent.

For the tank outlet, I am trying to make/buy a dip tube but when I place all the components together, the tube that would fit inside the male NPT fitting is either too small or too large. The opening is exactly 1.5" but the standard pipes do not fit inside.

The photo shows what i am trying to achieve. Ideally, I would have a barbed end but anything close to this will work. What am i missing?

 

[dlochner]

When I made the same modification on my Sabre 30, I used a Uniseal and not a tank fitting like you have.

Harken Traveler Car Repair

www.sv-secondstar.net

and an Amazon link to the Uniseal for 1 ½" ID pipe.

 

[Mr. Dave]

You need a pipe schedule. The basic idea is that the ID of a X" schedule 40 pipe is the states size, OD is greater. For instance, 4" ID on a 4" sched 40 pipe. Ish.

A 4" sched 80 pipe has the same OD as the sched 40, so thicker wall means reduced ID. You get the picture.

There's plenty more scheds than 40 & 80, so you need a better pipe schedule than I attached, that just gives you an idea of what you're up against. Elbows and couplings follow different rules. Sometimes.

There's also tubes, which follow different rules (OD tends to be actual, not nominal). It can get kinda ugly, but you'll figure it out, just find a real schedule, a fitting list, have a cool beverage of your choice, and enjoy the madness that is piping. Also consider the use of reducing couplings and street elbows.

As usual, McMaster-Carr can bevery helpful.

 

[Fredct]

Dlochner, I had considered the Uniseal product but i am concerned about the fitting leaking when boat it at high angle of heel. I note in your post that you recommend cross-venting so 2 separate vents? At the moment, I am planning for a single vent hole.

 

[Fredct]

Mr Dave, I see. HD only carries 40 and 80 and it does not fit. I need 1.5" OD exact. Will look into it now.

 

[dlochner]

Dlochner, I had considered the Uniseal product but i am concerned about the fitting leaking when boat it at high angle of heel. I note in your post that you recommend cross-venting so 2 separate vents? At the moment, I am planning for a single vent hole.

It's been a while since I did this job, so details are little foggy. The idea of using cross ventilation was mostly due to the tank design I had. It would be easier to add a second vent than to seal the old vent and install a new larger vent. Using 2 smaller vents would provide the same cross-section in the vent hoses and located across the tank would increase air flow through the tank. In the end, I left the single ½" in place and sold the boat.

In the several years I used the Uniseal, I never had a leak from the seal. If you search for the Uniseal company website they show the seal being used in the vertical walls of water tanks. It is a tight fit and it will be necessary to lubricate the dip tube with some dish detergent to get it to slide through the Uniseal.

 

[Project_Mayhem]

Mr Dave, I see. HD only carries 40 and 80 and it does not fit. I need 1.5" OD exact. Will look into it now.

Pipes have nominal sizing while tubing typically has exect ID and OD. Also, Dave knows his stuff

 

[Fredct]

Tubing? Ok, will look into it as well.

 

[dlochner]

Tubing? Ok, will look into it as well.

Tubing might be a poor idea. When the pump out starts to suck, it may collapse the tubing. A wad of TP could enter the tubing and clog it causing it to collapse. If tubing was used it would need to be heavy and reinforced to prevent collapsing. This would not solve your problem because 1 ½" hose is about 2 inches OD.

Metal tubing would also be a poor choice because the stuff in the holding tank can be acidic and it would react with the metal.

 

[Mr. Dave]

I mean, just sit down at your computer and dig through McMaster's offerings, tons of different tubes, pipes, fancy and boring plastics, stainless, aluminium, fittings galore. Entertaining perusing (for me), but the phone version sucks (relative to the real site at least)...

 

[Bob S]

I’ve used them on the side of plastic 55 gallon drums creating a filtering system and never had a leak. I used them in the holding tanks in two boats with no problems Peggie has recommended them for years.

 

[Fredct]

I’ve used them on the side of plastic 55 gallon drums creating a filtering system and never had a leak. I used them in the holding tanks in two boats with no problems Peggie has recommended them for years.

View attachment 185294View attachment 185294

Great photo. i think I am going to go there and thanks for reminding me about the gauge. I had forgotten. Will drill extra hole for that.

 

[dlochner]

Great photo. i think I am going to go there and thanks for reminding me about the gauge. I had forgotten. Will drill extra hole for that.

Consider a SCAD tank monitor, no need for an additional hole in the tank. Comes in single and 2 tank models.

Defender Search Results

 

[Peggie Hall HeadMistress]

Dlochner, I had considered the Uniseal product but i am concerned about the fitting leaking when boat it at high angle of heel. I note in your post that you recommend cross-venting so 2 separate vents? At the moment, I am planning for a single vent hole.

Uniseals do not leak when installed and fitted according to directions. I'll be happy to guide anyone who wants to use a Uniseal correctly. Buy it directly from Unseal...and I recommend calling them to do that instead of just getting online. That'll allow you to make sure you buy the correct size for your application UNISEAL

For the tank outlet, I am trying to make/buy a dip tube but when I place all the components together, the tube that would fit inside the male NPT fitting is either too small or too large. The opening is exactly 1.5" but the standard pipes do not fit inside.

If you order the tank with a diptube (it's not to too late to do that if they haven't already shipped the tank), Ronco will supply it connected to a hose fitting that has a 1.5" OD. It will not be installed...you'll insert it in the tank when it arrives. I strongly recommend doing that BEFORE bringing it aboard the boat.

You're welcome to give me a shout if you want some one-on-one help with this project.

--Peggie

 

[Fredct]

#Peggy, I had placed the order on hold yesterday so I can change it. I did not realize that Ronco could ship with a dip tube... it is not documented online as far as I could find.

I will repost later today when I have straightened this out one way or the other.

 

[Fredct]

For completeness. Called Ronco. They call it standing pipe. Alondra from Ronco working on it.

That said, HD sells a weldable 1.5" thin-walled trap extender for sink drains. OD is nearly 1.5" (12" long). Did a welding test with a piece of PVC: success. So in summary, we have 3 options:

1- Use Uniseal. Advantage - straight pipe can be used. May be difficult to install in tight spaces without head room (my case)
2- Get Ronco standing pipe
3- Make your own dip tube using SCD 40 1.5" male threaded + solvent wleded thin-wall trap extender

 

[dlochner]

For completeness. Called Ronco. They call it standing pipe. Alondra from Ronco working on it.

That said, HD sells a weldable 1.5" thin-walled trap extender for sink drains. OD is nearly 1.5" (12" long). Did a welding test with a piece of PVC: success. So in summary, we have 3 options:

1- Use Uniseal. Advantage - straight pipe can be used. May be difficult to install in tight spaces without head room (my case)
2- Get Ronco standing pipe
3- Make your own dip tube using SCD 40 1.5" male threaded + solvent wleded thin-wall trap extender

I would go with 1 or 2. Head room shouldn't be a big issue, install the stand pipe before you install the tank.

 

[Fredct]

in my boat, the opening inside the V-berth is small such that the fittings will need to installed once the tank is inside the compartment.

 

[Fredct]

Update and help needed - still dealing with pipes.
Tank on order. I got the 3 threaded fittings and Ronco will send the standing pipe as well so i have 2 options + I can always go with the Uniseal if everything else fails.

We have about 3-4 weeks of sailing left in the season so while I am waiting for the parts to come in, I used ozone generator inside the tank locker. Made a rather dramatic impact, short-lived I am sure.

Now I am upgrading my vent line to 1", as recommended in many places on this forum. My question is this: How can I safely enlarge the existing holes (about 7/8")?

I looked at videos of people drilling in fiberglass but they always start fresh with a small pilot etc. How do I do it with an existing hole that will not allow proper alignment of the pilot bit?

 

[dlochner]

There are several tricks here.

1. Place the ⅞" hole saw inside the larger hole saw. The small hole saw will serve as a guide. I've never done it this way, but have heard of it.

2. Hot glue a piece of scrap wood, ¼" ply wood works, behind the hole. This will guide the drill bit on the hole saw. The plywood will pop off afterwards. I've done this with a large hole saw, worked well.

3. Cut a plug the same diameter as the existing hole. Epoxy the plug into the hole. When cured, use a hole saw to cut a new hole. I've used this to enlarge the holes for transducers. Works well for thick sections of hull.

For your application where the hull is probably fairly thin, I'd use option 2. Besides, if you don't have a hot glue gun, now you have an excuse to buy one. Remember any job that requires a new tool is a job worth doing.