How many gallons is an RV black water tank?

Quick Answer

The size of RV black water tanks can vary greatly, but typically range from 30 to 50 gallons for most RV models. The black water tank holds wastewater from the toilet and sink drains. Knowing the tank size is important to gauge how often it needs to be emptied.

What is an RV Black Water Tank?

A black water tank is a wastewater holding tank in an RV that collects and stores sewage from the toilet and sink drains. It is part of the RV’s plumbing system. The black tank holds the wastewater until it can be emptied at a dump station or using a mobile pumping service.

Some key facts about RV black water tanks:

  • Stores wastewater from the toilet, sink, shower drains
  • Usually the largest of the waste tanks in an RV
  • Typically 30-50 gallons in size depending on RV model
  • Made from molded plastic or welded steel
  • Has a release valve to drain contents
  • Should be emptied when reaches 2/3 full

The black tank is completely separate from the fresh water tank that holds clean water for use in the RV. It also differs from the gray tank that stores wastewater from the shower and sinks.

Typical RV Black Tank Sizes

The size of the black water tank depends on the type and length of the RV. Here are some typical sizes:

  • Small travel trailers – 30-35 gallons
  • Mid-size travel trailers – 35-45 gallons
  • Large travel trailers – 40-50 gallons
  • Class C motorhomes – 35-60 gallons
  • Class A motorhomes – 50-100+ gallons
  • Fifth wheels – 50-75 gallons

Newer RVs tend to have larger tank capacities than older models. Larger RVs like motorhomes and fifth wheels need bigger tanks to hold waste for longer periods.

It’s important to know your RV’s black tank capacity to understand how often it will need to be drained. The more people using the toilet and sinks, the quicker the tank will fill up. RV tank sizes are usually listed in the owner’s manual or specs.

Checking Black Tank Level

There are a few ways to check the water level in your RV black tank:

  • Monitor panel – Most RVs have a monitor panel that shows tank levels
  • Tank sensors – Stick gauges or electronic sensors show exact tank content levels
  • Look in the toilet – Remove toilet and shine a light down into the black tank
  • Weighing – Use RV tank weighing scales to determine if tanks are empty or full

Using the monitor panel is the easiest way to get an estimate of black tank capacity used. More accurate electronic tank sensors can be added to get real-time readings from inside the tank.

Weighing the RV before and after dumping tanks is the most precise way to calculate black tank capacity in gallons. Subtract the post-dump weight from the pre-dump weight, then divide by 8.3 pounds per gallon of water weight.

Emptying the Black Tank

It’s essential to empty the black water tank regularly to prevent clogging and potential overflow. Follow these steps:

  1. Wear gloves and eye protection
  2. Connect sewer hose to outlet valve
  3. Place end of hose in dump station inlet
  4. Open black tank valve to begin drainage
  5. Allow tank to drain completely
  6. Rinse and flush black tank through the toilet
  7. Add tank deodorizer and cleaning agents as needed
  8. Close black tank valve and disconnect sewer hose

Experts recommend emptying the black tank when it reaches 2/3 capacity. This gives enough free space to allow proper drainage. Never let your black tank get completely full.

Look for dump stations at campgrounds, RV parks, rest areas, and fuel stations. Some RVs can also use mobile pumping services to empty their tanks.

Extending Time Between Draining

To maximize time between black tank dumps:

  • Use campground bathroom whenever possible
  • Take fast showers and limit water usage
  • Use biodegradable RV toilet paper
  • Add a tank deodorizer and treatment chemicals
  • Only flush waste and toilet paper
  • Use full hookup sites to connect to sewer

Limiting water usage reduces liquid going into the black tank. Special toilet papers dissolve faster than regular household TP. Chemical additives help break down solids.

When connected to a sewer at a full hookup site, tanks can be drained continuously without filling up. This allows for longer times between trips to the dump station.

Increasing Black Tank Capacity

If you find yourself needing to empty the black tank too frequently, there are ways to increase its usable capacity:

  • Use a macerator system – Liquifies waste allowing more storage
  • Add supplemental holding tanks – Install portable waste tanks
  • Replace fixed tanks – Have larger permanent tanks professionally installed
  • Use portable cassette toilets – Empty cassettes as needed

A macerator pump grinds and liquifies waste so more can be stored. Extra portable tanks are connected to the plumbing system to increase overall capacity. Replacing undersized, existing black tanks requires modification but adds permanent extra space.

Cassette toilets capture waste in removable cartridges that are dumped independently from the RV black tank. They can significantly increase time between having to empty the fixed black tank.

Black Tank Maintenance

It’s essential to keep the black tank clean and well maintained. Suggested maintenance steps include:

  • Use a tank deodorizer and frequent cleaning agents
  • Rinse and flush tank thoroughly when emptying
  • Inspect seals and fittings for leaks
  • Keep drain valve closed to allow beneficial bacteria growth
  • Use a wand to clean tank interior as needed
  • Dispose of waste properly, not on the ground

Chemical deodorizers and cleaners help control odor and breakdown tank waste. Rinsing the tank walls when dumping allows any stuck-on waste to dissolve. Check for leaks around plumbing fittings. Closing the tank between use promotes helpful bacterial growth. Monitor tank sensors for any changes indicating potential problems.

Proper maintenance keeps the black tank operating efficiently and prevents more serious problems from arising. Consult your owner’s manual for any tank cleaning guidance specific to your RV model.

Black Tank Problems

Some potential black tank problems and solutions include:

Problem Potential Causes Solutions
Odor Excess waste, vent pipe issues, insufficient chemicals, bacteria buildup Add deodorizer, clean tank, check vents, empty more frequently, flush with water
Clogs Solids buildup, foreign objects, root penetration Use wand to breakup solids, remove objects, install filter, flush with water
Leaks Cracked tank/pipes, loose fittings Check connections, test for cracks, replace components
Monitor Issues Sensor failure, wiring problems Test monitor panel accuracy, check sensors, inspect connections and wires
Slow Drain Clog, crimped hose, valve issue Use sewer hose supports, inspect valve operation, remove obstructions

Catching tank problems quickly can prevent more costly repairs. Know your RV black tank system well and perform regular monitoring and maintenance.

Using Public Toilets and Campground Bathrooms

Using public restrooms or shared campground facilities as much as possible reduces waste going into the RV black tank. This helps extend time between dump sessions.

However, be courteous of other guests. Don’t monopolize bathrooms or use campground facilities for all needs. It’s fine to use public facilities to quickly shower or use the toilet when convenient. But relying on them fully is usually poor etiquette when suitable onboard facilities are available.

Understand campground rules on bathroom usage as well. Most don’t mind occasional use, but excessive use or bathing may be frowned upon. Avoid inconveniencing fellow guests by overusing shared restrooms.

RV Black Tank Frequently Asked Questions

Get answers to common RV black water tank questions:

How often should I empty the black tank?

Empty the black tank at 2/3 full or when tank monitors show full indicators. For many RVs, that’s every 2-3 days of use. But monitor tank levels closely.

Do black tanks have level sensors?

Yes, most modern RVs have sensors to show black tank fill levels. Aftermarket sensors can be added easily to older RVs. The panel may show exact percentages or fractions full.

Should the black tank valve be left open or closed?

Keep it closed! This lets helpful bacteria grow to dissolve waste. Only open briefly at dump stations. Never permanently leave open.

Does my RV need tank treatments or deodorizer?

Yes, using RV waste tank treatments and deodorizers helps break down solids, control odors, and improve drainage. Consult your dealer for recommended products.

Can I add an extra black tank to increase capacity?

Yes, adding a supplemental waste holding tank can significantly boost capacity. Tanks are connected to existing plumbing. Install professionally for best results.

How do I add chemicals to the black tank?

Typically directly into the toilet bowl to rinse down into the tank. Some RVs have dedicated spray ports inside the tank. Follow product instructions carefully.


RV black water tanks typically range from 30-50 gallons for most travel trailers and motorhomes. Size varies by RV type and length. Knowing tank capacity helps gauge how often you’ll need to empty it. Add tank deodorizers and routinely inspect plumbing components. Only flush waste and toilet paper. Use public toilets when possible to extend time between dumping. Proper maintenance keeps the black tank operating efficiently.

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