How to Clean Caravan Water Tanks (Fresh + Grey)

Caravan water tanks are easy to ignore, right up until the water smells “off”, the tap starts sputtering, or the grey tank begins to announce itself every time you open a hatch.

The truth is, water systems get a workout on the road. You fill up from different sources, you park in heat, you bounce along uneven roads, and you sometimes leave the van sitting between trips. Over time, a thin layer of buildup can develop inside the tanks and lines (often called biofilm), along with sediment that settles at the bottom. None of this is unusual. It’s simply part of touring.

If you travel the way many Century Caravans owners do, mixing caravan parks with free camping, taking longer loops, and carrying water to stay self-sufficient, cleaning your tanks becomes less of a “deep clean chore” and more of a normal touring habit. The good news: it’s not complicated, and once you’ve done it once, it becomes quick and predictable.

This guide covers fresh water tanks (the water you use for drinking/cooking/showers) and grey water tanks (wastewater from sinks and showers), plus a simple routine to keep things fresh between big cleans.

Note: Always follow your caravan manufacturer’s guidance and any chemical product instructions. Never mix cleaning chemicals.

Fresh vs grey: what you’re actually cleaning

Fresh water tanks are about hygiene and taste. You’re trying to remove stagnant smell, biofilm, and sediment, then sanitise the tank and lines so water stays pleasant and safe to use.

Grey water tanks are about odour and buildup. They collect soap residue, food particles, and grime. If that sits warm for a few days, the smell can be impressive. A grey tank clean is less about “sterile” and more about keeping the system flowing and manageable.

They’re different jobs, and they respond best to different methods.

Part 1: Cleaning a freshwater tank

A proper fresh tank clean has three phases: drain, wash through, then sanitise. If you skip the sanitising step, you may remove the smell temporarily, but the underlying buildup can come back faster than you’d like.

1) Start by draining the system completely

Pick a time when you’re near a drain point, and you can flush water out responsibly.

Drain the fresh water tank, then open taps (hot and cold) to clear water from the lines. If your caravan has an external shower, don’t forget that line too. The goal here is simple: clear the old water so you’re not diluting the clean with leftovers.

2) Flush out sediment (the “unsexy” part that makes a big difference)

Even clean-looking water can leave grit and sediment behind, especially if you’ve filled from mixed sources. A basic flush helps lift that material out.

Refill the tank partway with fresh water, then drain again. If you’re doing this after a long trip (or you’ve been free camping and refilling often), doing this flush twice is worth it.

This is also the moment to quickly check any accessible filters (if your system has them). A dirty filter can make water taste odd, even after you sanitise.

3) Sanitise the tank and lines (without getting dramatic)

This is the step that actually deals with biofilm and lingering bacteria.

You can do this with:

• a purpose-made caravan tank sanitiser, or
• an appropriate diluted sanitising solution per your manufacturer’s guidance.

Whichever option you choose, the key is that the sanitiser must run through the tank and the lines, not just sit in the tank.

After adding the sanitising solution to the tank, top up with fresh water and run each tap until you can smell the sanitiser faintly at that outlet. Then leave the solution to sit for the recommended time (follow the product instructions). This “contact time” is what makes the process effective.

Once the time is up, drain the tank again.

4) Rinse thoroughly until the smell is gone

Now you’re removing the sanitiser itself.

Refill the tank with fresh water, run all taps (hot and cold), and drain. Repeat until the smell is gone and the water runs clear. This is where patience pays off. Rinsing properly is what makes the system pleasant again.

If you’re about to head off in your caravan (especially for a longer tour), finishing with a full tank of clean water is a nice way to start the trip feeling organised.

Why hot water matters (and what to do about it)

A lot of “my caravan water tastes weird” complaints actually come from the hot side of the system.

Once your fresh tank is clean, it’s worth running the hot water through properly during the rinse phase. You’re not trying to flush a tiny amount. You want clean water moving through the hot line so the whole system resets.

How often should you clean a freshwater tank?

It depends on how you tour, but a practical rhythm looks like this:

• After long touring loops (especially if you’ve filled from varied sources)
• After the caravan has been stored for a while
• Any time water smells or tastes “off”
• A couple of times a year as a preventative baseline

For people using their caravan regularly, the kind of touring a Venus owner might do across changing seasons, tank cleaning is usually a “start of trip” or “end of trip” habit, not something you wait to become a problem.

Part 2: Cleaning a grey water tank (the smell-control approach)

Grey tanks aren’t usually hard to clean. They’re just easy to neglect. And because they hold soap, food residue and grime, they can smell bad even when the tank isn’t “full”.

The goal is to prevent buildup from becoming a sticky, smelly layer.

1) Drain the grey tank completely (while it’s still warm if you can)

If you’ve just arrived at a dump point after driving, the contents are often warmer and move more easily. That makes rinsing more effective.

Drain fully, then give it time to empty properly. Rushing this step tends to leave more residue behind.

2) Rinse it out (more than once if needed)

A simple rinse goes a long way. If your caravan has a tank flush point, use it. If not, you can often rinse by running clean water through sinks and the shower briefly, then draining again.

If the grey tank smell has been building for a while, doing a rinse-drain cycle twice can reset it quickly.

3) Deal with the source, not just the symptom

Grey smell often comes from what goes down the sink, not the tank itself.

If you want less grey tank drama:

• wipe pans and plates before washing
• avoid tipping oily leftovers into the sink
• use sink strainers to catch food particles
• run a little extra water after washing up to push residue through

That small behaviour change makes a bigger difference than most people expect, especially on longer trips where you’re cooking regularly (which is exactly what many people love about touring caravans like the Venus range).

4) Use a suitable grey tank treatment if smells persist

If the tank still smells after a good rinse, a grey tank-friendly treatment can help. The main thing is to choose products that are designed for caravan plumbing and seals, and to follow the label instructions.

Avoid mixing products and avoid “kitchen chemistry”. Many unpleasant smells come from residue interacting with the wrong cleaner.

The simple maintenance routine that keeps tanks easy

Once your system is clean, the easiest way to keep it that way is to adopt a light routine that matches touring life.

Before storage (or after a trip):

• drain fresh water if the van will sit for a while
• drain grey water fully
• give the grey tank a quick rinse if you can

• On tour:
• don’t let grey water sit for days in hot conditions if you can avoid it
• if you’re doing a longer loop, plan a rinse/drain at a dump point every so often
• if you notice a change in fresh water smell/taste, do a quick flush earlier rather than later

This is especially relevant for travellers who love free camping: when you’re relying on your own water supply, the system feels better when it’s maintained, not “rescued”.

A note for Century Caravans owners

Century Caravans builds the Venus range for real touring — the kind where you actually use the onboard systems, not just the bed. If you’re doing longer trips or mixing park stays with off-grid nights, your water system becomes part of your comfort.

Keeping your tanks clean is one of the simplest ways to make touring feel “easy”: taps smell normal, showers drain properly, and the van stays pleasant to live in, which is exactly the experience people are chasing when they invest in a proper touring caravan.

FAQ

Can I drink water from my caravan fresh tank?

Many people do, but it depends on your tank hygiene and water source. If you’re unsure, use filtered water for drinking and keep your tank cleaning routine consistent.

Why does my caravan water smell after storage?

Stagnant water and warm conditions encourage buildup and odour. A drain + sanitise + rinse cycle usually fixes it.

How do I stop grey tank smell?

Drain regularly, rinse at dump points, minimise food/oil residue going down the sink, and treat the tank if needed.

Should I leave fresh water in the tank between trips?

If the caravan will sit for a while, many travellers prefer draining it to avoid stagnation. For short gaps between trips, it’s often fine. But if smell develops, clean earlier.