Class A Customs Fitting Helps and Examples for Water Tanks and Plumbing

Posted by on 4/4/2022 to Fresh and Gray Water Tanks

All water tanks we carry must be vented, they are not pressurized tanks.
Have a certified technician install all parts to prevent product damage and personal injury.

Tank must have a large enough opening for air to freely move in and out of tank, this is called "venting" the tank. If tank is not properly vented tank will explode when filled or implode when emptied.
A garden hose is a pressurized water line, do not make a secured connection to the water tank with a pressurized line. Tanks need to be gravity feed, this allows for air to escape while the water is going into the tank.

Our Basic Plumbing Diagram shows how an RV or food unit can be set-up using a gravity fill dish. Gravity Fill Dish Instructions

Under Sink Gray Tank Set-up Examples

For Gray water tank use you can use any of Class A Customs water tanks, Gray and Waste tanks do not need to be food safe.

To feed directly into the tank you can use a Uniseal Fitting that allows you to place a fitting anywhere in the tank, this is very helpful for concession trailers that want to put the tank under the sink.

Because the Fresh/Gray tanks come with only 1.5" NPT Female fittings and .5" NPT Female fittings built into the tank end user will need to get connecting fittings and adapters that pipe may be installed into.

Depending on the size of the pipe you are using you will need different connecting fittings and adapters, Class A Customs only carries a 1.5" PVC Adapter Fitting - White this may not work for your application, please verify before purchasing.

Can I have the fittings moved or extras added?
We only offer custom fittings on water tanks if ordering a qty of 50+ tanks (single type of tank) per order. Uniseal Fittings allow you to place a fitting in any location on a water tank.

Our WATER TANK HELPS PAGE located at the top of each page gives helpful tank installation information along with answers to frequently asked questions.

At this time Class A Customs only installs the following fittings into our Fresh / Gray tanks

1.5" NPT Female - fitting is closed
use a razor knife to cut membrane out, easiest when cut in halves

Fittings and Hoses We Offer That Fit 1.5" NPT Tank Fitting

1.5" NPT Male Thread X 1.25" Hose Barb Plastic Fitting - Gray

Can be used with 1.5" Fitting on tank to connect to 1.375" Hose

1.5" PVC Adapter Fitting - White

Can be used with 1.5" Fitting on tank to connect 1.5" PVC Pipe for draining fresh or gray water tank

1.375" (1-3/8") Food Grade Water Hose
1.375" hose can be used with the fill dishes and the Loose Fitting / Fixture - 1.5" Thread x 1.25" Hose Barb Fitting - Gray
1.375" hose can not be used with spouts on tanks.

.5" NPT Female - fitting is open

Fittings and Hoses We Offer That Fit .5" Tank Fitting

.5" NPT Male Thread X Hose Barb Plastic Fitting - Black

Can be used with .5" Fitting on tank with .5" Hose for Fill Dish Vents and Water Pumps

.5" Food Grade Water Hose

.5" Hose can be used with the fill dishes vents and the water pumps we sell.

1.25" Outer Diameter x 2" Long Smooth Pipe / Boss Fitting - Spout
glues does not stick to pipe, it can not be sealed or capped
you will need to use the 1.25" Hose with Clamp

Hose We Offer That Fit 1.25" Tank Fitting

1.25" (1-1/4") Food Grade Water Hose
1.25 hose hose can be used with the gravity dishes and spouts/boss fittings on tanks.
1.25 hose does not fit the Loose Fitting / Fixture - 1.5" Thread x 1.25" Hose Barb Fitting - Gray

Class A Customs Basic Plumbing Kit

Designed for Class A Customs Stock Fresh Water Tank set-up using a Fill Dish (fill dish not included)

This is for Fresh Water Systems Only - Not to be used for Gray or Waste Water Systems

Kit does not fit a SPOUTED Water Tank

EXAMPLE PLUMBING FOR FRESH WATER SYSTEM

Where are the fittings located on the tanks?
Are there fittings on both ends of the tanks?
Please look at the photos of each tank as fitting placement can vary by tank, typically fittings are all located on one end of the tank.

How do I get the large fitting out?

Are these punch out fittings?

Each tank will come with at least one vent hole made during the manufacturing process (this is not the vent hole for when using the tank), a permanently mounted patch is placed over this hole, this is not a fitting and does not unscrew.

Can I cut a hole in the tank and glue another fitting in?

There is glue flaking on my tank isn't this from gluing the fitting in?

No, fitting are spun welded into the tank, friction between the fitting and the tank causes both to melt and permanently seal, no additional glues or sealants are used to install the fittings. The residue left by putting the fittings in place is part of the material the tanks and fittings are made from and may spider crack or flake off over time, this in no way harms the tank or causes any usage issues. To add fittings or repair a damaged fitting we now offer Uniseal Fittings which allow you to put a fitting in any location, sizes range from .5" - 3"

Can I hook more than one tank together?

Yes, sometimes this is called "daisy chaining" the tanks together. You will need to check with a certified plumber to see what fittings and set-up will work best for your unit, remember to vent each tank.
You can hook the tanks together using the provided fittings or by making a fitting in the side of the tank using a Uniseal fitting.

What fittings will I need for my plumbing?

We are not aware of how to set-up your tank, set-up will vary by each application this is something you need to research. Have a certified technician install all parts to prevent product damage and personal injury. Please view our Plumbing Category for information on loose fittings we carry. Be sure to Sanitize Tank before installing.

It is recommended to use plastic NPT male fittings with plastic female NPT fittings to avoid damaging the threads, metal thread fittings can crush the plastic threads. Very little, if any, pipe thread tape is needed using too much pipe tape will damage the threads. We do not recommend pipe dope as you can not remove the fitting later, if used be sure to use a food safe brand. Do not over-tighten fittings as damage will occur.

Due to the vast amount of plumbing applications and set-ups needed for RV's, concession trailers, tiny houses and more we aren't aware of what all items you will be needing for your project.

We are including some helpful links to items you may be able to use for your application, we do not sell these items - you are going to a new website by clicking the links. As with all purchases be sure to verify what you will be needing before purchasing.

Nylon Tube & Hose Fittings

Tubing, Hose & Fittings

3/8" Hose Barb x 1/2" MNPT Nylon Male Adapter

1/2" MNPT Nylon Plug with Square Head

Suction Line Strainer that Fits Over 1/2" NPT

Only use this with tanks that will overflow outside of your unit, you do not want to overflow inside of unit.

Dometic Universal Holding Tank Cleanout Kit

Oatey® 1.5 in. NPT ABS In-Line Vent

Straight, Black Plastic Tank Vent

The fill dish is located on the outside of your unit so that you can easily add water to your fresh water tank without the need of opening a compartment or climbing under your unit. The fills dish also includes a small vent that allows you to connect your water tank vent to the outside of the unit, if your tank overflows it will overflow outside your unit. You can find the fill dishes in the Plumbing Category.

For adding water to the Fresh / Gray Water Tank you need a Gravity Fill Dish
the food safe garden hose rests in the fill port on the fill dish - it does not screw onto the port
this is a non-pressurized fill

For using water directly from a food safe garden hose you need a City Fill Dish
The plumbing will bypass your water tank and hook directly to your water heater and faucets.

The food safe garden hose makes a sealed connection on the fill dish and the water supply is pressurized.

This is a pressurized line and can NOT hook to your water tank - pressurizing the tank will cause the tank to explode, fittings to pop-out, cracks to tank, etc.

Units that have metal water tanks can use city fill dishes because the metal tank can withstand the pressure, Class A Customs water tanks can not be pressurized.

We carry Gravity Fill-Dishes, City Fill-Dishes and Combo Fill-Dishes that have both gravity and city, the benefit of having both is you can have a water tank of fresh water but if you go to a location that supplies pressurized water (campground - fair - etc.) you do not need to use your water tank supply of water you can simply use the water provided. Be sure to look at the provided example plumbing diagram for more reference.

For my application I am not using a fill dish.

For gravity feeding you can place a larger fitting such as a PVC elbow in the tank and allow your hose to rest in this when filling, do not make a secured/sealed connection as this would then be pressurized.

You will still need to vent the tank, this can be as easy as placing a fitting with a screen secured over it. Be aware that if you overfill the tank the excess water will exit the vent fitting, placing the vent fitting overflow to an outside location is recommended. Be sure to screen over the vent fitting overflow to prevent anything from entering the tank. Do not over-tighten fittings as damage will occur.

Examples of Items to Vent Tanks - We do not sell these products they can be found online
Oatey® 1.5 in. NPT ABS In-Line Vent
Straight, Black Plastic Tank Vent

For my application I am going to use a pressurized line to the tank.

This will void any warranty on the tank. Turning a garden hose on half way does not work because you can control the amount of water flowing but not the pressure in the line, leaving the tank to fill risks exploding the tank. Examples of Fittings you could use, depending on your application.

I need a clean-out hole for my tank.
We do not offer clean-out ports at this time but there are many options online that allow you to install the needed clean-out port.

Example Dometic Universal Holding Tank Clean-out Kit

Can I hook more than one tank together?
Yes, sometimes this is called to "daisy chain" the tanks together. You will need to check with a certified plumber to see what fittings and set-up will work best for your unit, remember to vent each tank.

I bought a fitting from my local hardware store and it won't fit.

Be sure you are using NPT fittings and getting the correct sizes. Do not over-tighten fittings as damage will occur. It is recommend to use plastic fittings with the plastic fittings installed in the tank to prevent damage to the fitting threads.

National Pipe Threads (NPT)
Pipe sizes do refer to physical dimensions, but the plumbing industry standard for the sizes of pipe is not always as straight-forward as measuring the pipe. Measuring the pipe will oftentimes mislead you into choosing the wrong pipe, so do take care. The "pipe thread size" as shown in column 3 of the table below is measured and based on the inside of the pipe. But, to actually determine the size of a pipe, the outside diameter of each pipe or fitting must be measured and compared to the table for size identification. For example, a 3/4" NPT pipe thread has an outside diameter of 1.050 inches. Each thread size has a defined number of threads per inch (TPI). The 3/4" NPT pipe thread has 14 threads per inch. Both the TPI (threads per inch) and OD (outside diameter) of the thread are required for positive identification of thread size because several sizes have the same TPI.

Male threads: Measure the outside diameter of the large portion of the thread at "A"; Find figure nearest this dimension in column 1 or 2 of chart. The dimension in column 3 will be your nominal pipe thread size.

Female Threads: Measure top diameter of thread at "B"; Find figure nearest this dimension in column 1 or 2 of chart. The dimension in column 3 will be your nominal pipe thread size.

Q."What does 'nominal' mean?"
A. Nominal is the term used to describe pipe and fitting measurements in plumbing. Nominal refers to the inside diameter of the pipe which varies by wall thickness of the pipe.

Q."Ok, so IPS pipe sizing isn't actually a dimension. So what about the fittings?"
A. Pipe fittings are "sized" by the "size" pipe they fit. So, for example, a 1/2" IPS fitting would fit 1/2" IPS pipe.

National Pipe Threads (NPT) have tapered threads. These are the most common threads used for general purposes. NPT threads are designed with a 60 degree thread angle, and are used for joining and sealing pipe to fittings in low pressure air or liquids and also mechanical applications. The tapered thread is 3/4" over one foot of length. Tapered threads are deeper at the end of the pipe and are increasingly shallower the further they are from the end of the pipe. The taper on the pipe only allows the pipe to screw inside the fitting until it is forced to stop because of the taper. The distance the pipe can be screwed into the fitting is specified by the ANSI standard. After tightening with a wrench the threads may have slight spaces between the pipe and fitting which could cause a leak so a pipe sealant must be used to ensure any gaps are filled.

The Dry-seal thread (NPTF) also have tapered threads. NPTF threads are used when the application is such that pipe sealing compounds may fail due to higher heat or pressure than normal NPT threads can withstand. The threads are designed to seal mechanically by slightly, but sufficiently, crushing the threads when tightened with a wrench. This allows for joining the pipe and fitting without sealants.

The NPT and NPTF threads can be interchanged if sealants such as PTFE tape or suitable pipe joint compounds are used. None of the other thread standards are fully interchangeable (GHT, NST, BSPT, NPSI, etc.) Female NPT threads can be designated as "FPT" or "FIP" and male NPT threads can be designated as "MPT" or "MIP".

National Standard Free-Fitting Straight Mechanical Pipe Threads (NPSM) have straight threads which are only used for joining. A washer or gasket is needed to seal this type of threaded connection.

There are also three less common thread types used in the plumbing industry. The Garden Hose Thread (GHT) and the Fire Hose Thread (NST) have coarse threads. The seal is made with a gasket or washer and are used mainly for attaching (joining) hoses to valves quickly, without the use of a wrench. The British Standard Taper Pipe Thread (BSPT) has a 55 degree thread angle (NPT are 60 degree) and is used internationally as a standard thread for joining steel pipes.

Waste Tank Venting and Plumbing

Class A Customs Black Water Tanks only come with the outlet the end user will determine where the inlet and vent will need to be placed and install.

Grommet (not food safe - waste tank use only) or Uniseal (food safe - fresh/gray/waste use) will secure inlet/vent pipe with no adhesives needed.

Use correct size hole saw bit (listed on item page) in order to drill a hole in the tank and place Grommet or Uniseal in hole, piping is then placed in fitting with no glues or adhesives necessary.

Waste Water Tank Installed Outlet
Black Waste Tanks - 3” ABS Female Pipe - outlet can not be moved -
Gray Waste Tanks - 1.5" ABS Female Pipe - outlet can not be moved - smaller outlet this tank is for dirty water from shower, handwashing, dish-washing

Do Not over-tighten fittings damage will occur.
Dump Valves are not connected directly to the Waste Tank ABS Outlet Fitting, the ABS Outlet Fittings are female fittings and the dump valves are also female fittings, they do not connect.

Use PVC or ABS pipe to connect to the 3" ABS Outlet Fitting installed on the waste tank, the dump valve is then connected to the pipe.

We do not sell glues, Examples Oatey 4-fl oz Green PVC/Abs Transition Cement