Plumbing Systems for 7x16 Trailer Conversions
A 7x16 trailer has room for a real plumbing system—full kitchen sink, hot water, shower, and toilet. Here's how to plan it.
A 7x16 cargo trailer plumbing system typically includes a 20-40 gallon freshwater tank, tankless propane water heater, shower, composting toilet, and 15-30 gallon greywater tank, costing $1,640-$3,650 in DIY materials. Professional installation adds $1,500-$3,000 in labor, bringing the total to $4,000-$7,000 installed. Emery Custom Builds designs 7x16 plumbing systems with proper tank sizing and weight distribution for safe, comfortable towing.
What Plumbing Can You Fit in a 7x16 Cargo Trailer?
With about 112 square feet of floor space, a 7x16 cargo trailer can support a full plumbing system comparable to what you'd find in a van conversion or small RV. That means a pressurized water system, hot water on demand, a shower, and a dedicated toilet—all without feeling like you're showering in a closet.
The extra space compared to a 6x12 means you can carry more water, fit larger tanks, and dedicate a proper section of the trailer to a wet bath or bathroom area. It also means more weight, so tank sizing is a balance between capacity and tow vehicle limits.
Typical 7x16 Plumbing Setup
Freshwater Tank
20–40 gallons. Most builds use a 30-gallon tank—enough for 3–5 days of normal use for two people. Mounted under the trailer or in a cabinet, depending on layout.
12V Water Pump
A Shurflo or similar 12V demand pump provides pressurized water throughout the system. Draws 3–7 amps depending on the model. Automatically activates when you open a faucet.
Water Heater
Tankless propane water heater for on-demand hot water. Compact wall-mount units heat water as it flows through—no storage tank needed. Standard for builds with a shower.
Kitchen Sink
Standard bar sink or RV kitchen sink with a single-handle faucet. Hot and cold water lines from the pump and water heater.
Shower
Dedicated stall or wet bath area with a shower head, drain, and waterproof walls. Typical wet bath is 3x5 feet or 4x4 feet. Drains to the greywater tank.
Composting Toilet
Nature's Head or Airhead composting toilet. No water required, no black tank, minimal maintenance. Uses a small 12V fan for venting.
Greywater Tank
15–30 gallons mounted underneath the trailer. Collects all drain water from sink and shower. Dumped at RV dump stations.
How Big Should Your Freshwater Tank Be?
How much water you carry depends on how you camp and how many people are on board:
- • 20 gallons: Good for weekend trips or solo camping. Lasts 3–4 days with conservative use. Weighs 166 lbs full. Leaves more room for other systems.
- • 30 gallons (most common): Covers 3–5 days for two people. Weighs 250 lbs full. The sweet spot for most 7x16 builds—enough range without maxing out your tow capacity.
- • 40 gallons: Extended boondocking or full-time living. Lasts 5–7 days for two people. Weighs 333 lbs full. Only go this large if your tow vehicle and trailer axles can handle the extra weight.
Pro tip: Mount the freshwater tank low and centered (under the trailer or near the axle) to keep weight distribution balanced. An off-center or high-mounted tank affects towing stability.
What Are the Best Hot Water Options for a 7x16?
If your build includes a shower, you need a way to heat water. Here are the options for a 7x16:
Tankless Propane Water Heater
$200–$600
The most common choice. Wall-mounted units (Camplux, Girard, Eccotemp) heat water on demand as it flows through the unit. No storage tank, no wasted energy heating water you're not using. Requires propane and venting to the outside. Flow rate of 1–2 GPM is plenty for a trailer shower.
Small Tank Water Heater (6 gallon)
$300–$700
A traditional RV-style water heater stores 6 gallons of hot water. Takes up more space than tankless but provides consistent water temperature. Can run on propane, electric (shore power), or both. Common in builds that prioritize comfort and campground use.
Electric Tankless (Battery Powered)
$200–$400
Possible but power-hungry. A small electric tankless heater draws 1000–1500W. Only practical with a large battery bank (400Ah+) and generous solar. Most builders go propane instead to save battery for other things.
Can You Fit a Real Shower in a 7x16 Trailer?
A 7x16 trailer can fit a proper shower. Two main approaches:
- • Wet bath (shower + toilet in one room): The most space-efficient option. A 3x5 or 4x4 foot area with waterproof walls, floor drain, shower head, and a composting toilet. Everything gets wet when you shower—toilet and all. Common in van and trailer builds. Takes 15–20 sq ft.
- • Separate shower stall: A dedicated shower space apart from the toilet area. Uses more floor space but keeps the toilet dry. More comfortable for daily use. Requires a larger trailer layout commitment.
Waterproofing is critical. FRP (fiberglass reinforced panels), PVC wall panels, or marine-grade materials keep water from reaching the insulation and wood framing. A shower pan or fully sealed floor with a proper drain ensures water goes to the greywater tank, not into the subfloor.
What Toilet Works Best in a 7x16 Trailer?
A composting toilet is the go-to for 7x16 trailer builds. Here's why—and what else is available:
Composting Toilet
$800–$1,500
Separates liquids and solids. No water needed, no chemicals, no black tank. A small 12V vent fan handles odor. Nature's Head and Airhead are the standard. Empty the solids bin every 4–6 weeks for two people. Dump the liquids jug every 2–3 days. Simple, low-maintenance, and widely proven in van and trailer builds.
Cassette Toilet
$100–$300
A portable toilet with a removable waste cassette. Uses water for flushing and chemical treatment for the waste tank. Pull out the cassette and dump at any RV dump station. Cheaper than composting, but you're dealing with chemicals and more frequent dumping.
Black Tank (RV-Style)
$300–$800
A permanent waste tank with a flush toilet. Requires a water connection, a large tank (15–40 gallons), and dumping at RV stations with a sewer hose. Heavy, complex, and adds plumbing lines. Most trailer builders avoid this unless mimicking a full RV setup.
How Do You Handle Greywater in a 7x16 Trailer?
Every drop of water from your sink and shower needs somewhere to go:
- • Tank size: Match your greywater tank to your freshwater capacity. A 30-gallon fresh tank should pair with at least a 20–30 gallon greywater tank. If your greywater fills up before your fresh runs out, you're stuck.
- • Mounting: Underneath the trailer, between the frame rails. Gravity-fed from sink and shower drains. Make sure there's enough clearance for ground obstacles.
- • Dump valve: A gate valve on the bottom of the tank lets you dump at RV dump stations via a short hose. Quick and clean.
- • Winter considerations: If you camp in freezing temperatures, the greywater tank needs heat tape or insulation to prevent freezing. A frozen greywater tank means no drains work.
How Much Does a Complete 7x16 Plumbing System Cost?
Professional installation adds $1,500–$3,000 in labor. A full plumbing system with hot water, shower, composting toilet, and proper greywater management runs $4,000–$7,000 installed.
How Do You Get Started with Your Plumbing System?
Plumbing affects your layout, your weight distribution, and your daily comfort on the road. A consultation helps us figure out the right tank sizes, water heater, and toilet setup for how you actually plan to use the trailer. We'll design a system that works and fits your budget.
Related guides: 7x16 Conversions · Plumbing Systems · 7x16 Electrical · 7x16 Cost Breakdown · 7x16 Interior
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