What Is Gray Water?
Gray water is all the wastewater from your RV that isn't from the toilet — kitchen sink, bathroom sink, and shower. It contains soap, food particles, grease, hair, and personal care product residue. It's significantly cleaner than black water (which contains human waste), but it still contains bacteria and isn't safe for direct disposal in most regulated areas.
Most RVs have one gray tank, though larger coaches sometimes have two — a separate kitchen tank and a bathroom tank. The bathroom sink often drains into the black tank rather than the gray tank on older RVs, so check your manual.
| Tank Type | Sources | Relative Cleanliness | Dump Requirement |
|---|---|---|---|
| Fresh water | City water / tank fill | Clean (potable) | N/A — supply tank |
| Gray water | Sinks, shower | Dirty but no sewage | Dump station or per local rules |
| Black water | Toilet only | Sewage | Always use dump station |
Why Gray Tanks Smell (And How to Fix It)
Gray water smells worse than most new RVers expect. The culprits are food waste, grease, and soap scum that decompose in a warm tank. A gray tank that smells like a sewer drain is common but entirely preventable.
Prevention: What Goes Down the Drain Matters
- Scrape food off plates before washing — food particles are the #1 cause of gray tank odor. A simple sink strainer catches most of it.
- Avoid pouring grease down the drain — grease coats the tank walls and decomposes slowly, creating persistent odor.
- Use biodegradable, low-suds soaps — Campsuds and Dr. Bronner's are popular among RVers. Conventional dish soap creates foam that traps odor-causing residue.
- Keep the valve closed — same principle as the black tank. An open valve lets liquid drain while residue dries and concentrates. Keep it closed and dump deliberately.
Treatment: Enzyme Drain Maintainers
Enzyme-based drain treatments (like Unique RV Digest-It or Happy Campers) added to the gray tank after each dump break down food residue and soap scum before they become odor problems. A tablespoon of baking soda in the kitchen drain daily also helps buffer pH and reduce odor.
Gray Tank Full While Camping: Your Options
The gray tank fills faster than the black tank for most RVers — and running out of gray capacity mid-trip is a common problem. Here's what to do:
At a Campground with Hookups
If you're at a full-hookup site, you can technically leave the gray valve cracked or fully open — gray water is safe to discharge into the campground's sewer system. This is different from leaving the black valve open (which dries the tank). Some RVers manage gray capacity this way, though it does create the residue buildup issues mentioned above.
At a Campground with a Dump Station
Pull to the dump station and dump the gray tank. You don't have to dump the black tank at the same time if it's not full yet, but it's usually worth doing both while you're there.
Boondocking / No Hookups
Options when boondocking: use a portable gray water tote tank (like the Barker 4-Wheeler), reduce water usage (navy showers, dish basin instead of running water), or check if your location permits responsible gray water dispersal (see the FAQ below). Many boondockers use a portable 20–30 gallon tote that they haul to a dump station without moving the RV.
How to Dump the Gray Tank
Gray tank dumping is simpler than black, but the sequence matters:
- Connect your sewer hose to the dump station
- Dump black water first (if needed)
- Open the gray valve — let it drain completely
- The gray water flushes and rinses the sewer hose for you
- Close the valve, disconnect, and cap both the hose and RV outlet
Extending Gray Tank Capacity
If you consistently run out of gray capacity, these strategies help:
- Navy showers: Wet down, turn water off, soap up, rinse. Cuts shower water use from 10+ gallons to 2–3 gallons.
- Dish basin: Wash dishes in a small basin instead of with running water. The collected water can be disposed of at a dump station.
- Portable tote tank: A 20–35 gallon portable holding tank extends your effective gray capacity significantly and can be towed to a dump station separately.
- Collapsible water bucket: For small amounts of hand-washing water, a collapsible bucket that you dump at a designated area is a simple boondocking solution.
Frequently Asked Questions
It depends on where you're camping. On dispersed BLM and National Forest land, gray water disposal is generally permitted if it's scattered (not pooled), at least 200 feet from water sources, and uses biodegradable soap. In most campgrounds, state parks, and national parks, you must use the dump station. California prohibits all gray water ground disposal regardless of location. Always check local regulations before dispersing gray water.
It's not ideal but it's acceptable for the gray tank — unlike the black tank, leaving the gray valve open won't cause a pyramid plug problem. However, it does allow soap scum and food residue to bake onto tank walls over time, contributing to odor. The better practice is to leave it closed and dump every 2–3 days. If you leave it open, do a thorough tank flush with enzyme treatment periodically.
If you use biodegradable, phosphate-free soap (like Campsuds), gray water from sinks and showers can water non-edible plants on most federal lands where dispersal is allowed. Don't use gray water containing harsh chemicals, bleach, or conventional dishwashing detergent on plants. Never use gray water on edible crops due to potential bacterial contamination. Check local regulations — household gray water reuse rules vary significantly by state.