If you own or are renovating a 1978 double wide mobile home with two bathrooms, chances are you’ve run into plumbing issues—or you’re planning ahead to avoid them. Finding the right 1978 double wide mobile home two bathroom toilet plumbing diagram can feel like searching for a needle in a haystack. But don’t worry—you’re not alone. Many homeowners struggle with outdated schematics, corroded pipes, or confusing layouts. In this guide, we’ll walk you through everything you need to understand your system, troubleshoot common problems, and even locate or reconstruct your plumbing diagram with confidence.
Why Is the 1978 Double Wide Plumbing Layout Unique?
Mobile homes built in the 1970s—especially 1978 double wides—followed early HUD (U.S. Department of Housing and Urban Development) standards, which were less stringent than today’s codes. These homes often used polybutylene (PB) piping or galvanized steel, materials now known for corrosion and failure over time.
Did you know? According to the National Association of Home Builders (NAHB), nearly 60% of mobile homes built between 1976 and 1993 used polybutylene piping—now widely discontinued due to high leak rates.
Unlike site-built homes, mobile home plumbing is factory-installed underneath the floor, making repairs more complex. In a two-bathroom double wide, plumbing lines typically run parallel along the marriage line (where the two sections join), with each bathroom served by its own branch—but sharing a main waste and vent stack.
Where to Find Your Original Plumbing Diagram
Unfortunately, manufacturers rarely released public plumbing schematics for 1978 models. However, you can try these verified methods:
Check the home’s data plate Located near the main electrical panel or inside a kitchen cabinet, this metal tag lists the manufacturer, model, and serial number—critical for requesting archival documents.
Contact the original manufacturer Brands like Fleetwood, Champion, Skyline, or Redman may still have records. Even if the company is defunct, successor firms (e.g., Skyline Champion) sometimes retain old blueprints.
Search public archives Some states’ housing departments keep historical mobile home documentation. For example, Florida’s Department of Highway Safety and Motor Vehicles maintains model approval records.
Use generic diagrams as a starting point While not exact, standardized layouts for late-1970s double wides can help you reverse-engineer your system (see section below).
⚠️ Warning: Never rely solely on online “free diagram” PDFs—they’re often inaccurate or generic.
Understanding the Two-Bathroom Plumbing Layout
In a 1978 double wide with two bathrooms, plumbing is typically arranged as follows:
Component
Description
Freshwater Supply
Cold and hot lines (usually ½” copper or PB) run under the floor, branching to each bathroom sink, shower, and toilet fill valve.
Drain-Waste-Vent (DWV)
2″ or 3″ ABS or cast iron pipes carry waste. Each toilet connects to a 3″ drain; sinks and showers use 1.5″–2″ lines. All tie into a main stack vented through the roof.
Marriage Line Junction
The two halves join here. Plumbing lines must align precisely—misalignment causes leaks or blockages over time.
Toilet Placement
Most 1978 models placed toilets back-to-back or on opposite walls. Each has its own flange and closet bend.
Typical Toilet Plumbing Path (Step-by-Step)
Toilet tank fills via a 3/8″ supply line from the main cold water branch.
Flush valve releases water into the bowl, creating a siphon.
Waste travels through a 3″ wax-sealed closet flange into a 3″ PVC or ABS drain pipe.
Drain slopes ¼” per foot toward the main waste line.
Main waste exits under the home (often near the marriage line) into a sewer or septic system.
A vent pipe (usually 1.5″–2″) runs vertically through the roof to equalize pressure.
💡 Pro Tip: If your toilet gurgles when the shower runs, you likely have a blocked vent—a common issue in older mobile homes due to debris or rodent nests.
Common Plumbing Problems in 1978 Double Wides
Issue
Likely Cause
Solution
Low water pressure
Corroded galvanized pipes or clogged aerators
Replace with PEX or copper; clean fixtures
Sewer smell in bathroom
Dry P-trap or cracked vent
Pour 2 cups of water monthly into unused drains; inspect roof vent
Toilet won’t flush fully
Partial clog or weak flapper
Use a closet auger; replace flapper with 1970s-compatible model
Leaks under floor
Failed PB pipe joints or rusted steel
Repipe entire section with PEX-A (recommended for mobile homes)
According to a 2022 Mobile Home Repair Survey by MHInsider, 73% of plumbing-related service calls in pre-1985 double wides were due to pipe material failure—not poor installation.
How to Create Your Own Plumbing Diagram (If You Can’t Find It)
Don’t have the original? Build one yourself:
Turn off main water supply and drain lines.
Remove access panels under sinks and near toilets.
Trace each pipe with colored tape (blue = cold, red = hot, black = drain).
Sketch on grid paper, noting distances from walls and marriage line.
Label all fixtures and pipe diamaters.
Take photos for digital backup.
You can also use free tools like SketchUp Free or SmartDraw to digitize your layout.
📌 Note: Always verify pipe materials before cutting—polybutylene looks like copper but is gray plastic. Confusing the two can cause costly mistakes.
Q1: Are plumbing diagrams for 1978 mobile homes public record? No. Manufacturers treated them as proprietary. However, some state housing agencies may have approval schematics on file if the model was licensed for sale in that state.
Q2: Can I replace my 1978 toilet plumbing with modern PEX? Yes—and it’s highly recommended. PEX is flexible, freeze-resistant, and easier to install in tight underfloor spaces. Use PEX-A with expansion fittings for best results in mobile homes.
Q3: Why do both toilets clog at the same time? This usually indicates a blockage in the main drain line after the two bathroom branches merge—often near the marriage line or under the kitchen. Use a 50-foot drain auger or call a plumber with a camera scope.
Q4: How do I locate the sewer cleanout? In most 1978 double wides, it’s a 3″–4″ capped pipe under the home near the bathroom wall, often accessible via a removable skirting panel. If buried, look for a slight mound in the soil outside.
Q5: Were vent pipes required in 1978 mobile homes? Yes. HUD Code (effective June 1976) mandated venting for all plumbing fixtures to prevent siphoning and sewer gas entry. Look for a 1.5″–2″ PVC pipe penetrating the roof near bathroom walls.
Q6: Can I add a third bathroom to a 1978 double wide? Technically yes, but it’s not advisable. The original septic or sewer line wasn’t designed for extra load, and structural support under floors may be insufficient. Always consult a licensed mobile home contractor first.
Conclusion
Navigating the plumbing system of a 1978 double wide mobile home with two bathrooms doesn’t have to be overwhelming. With the right knowledge—and a reliable1978 double wide mobile home two bathroom toilet plumbing diagram (or the ability to create one)—you can tackle repairs, prevent disasters, and even increase your home’s value.
Whether you’re unclogging a drain, replacing old pipes, or just curious about your home’s infrastructure, understanding your layout is the first step toward confident homeownership.
👉 Found this guide helpful? Share it on Facebook, Pinterest, or Reddit to help fellow mobile home owners! And if you’ve successfully mapped your plumbing, we’d love to hear your story in the comments below.
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