A Question Worth Asking Before You Drop One In
Most customers who try Blop have no issues at all — they open the cistern lid, place Blop upright at the bottom, and that's it. It just works.
But we've also heard from a small number of customers whose cistern setup made things a little more complicated. So this article is our attempt to give a clear, honest answer: what cisterns work well with Blop, and what should you check before you start?
The Short Answer
Blop is compatible with the vast majority of toilet cisterns found in Australian homes. This includes:
Close-coupled cisterns — the most common type in Australia, where the cistern sits directly on top of the toilet pan. These typically have a good amount of internal space and work well with Blop.
Connector (link) cisterns — mounted slightly higher on the wall with a short flush pipe connecting to the pan. Usually fine, as long as there's enough clearance inside.
Concealed/in-wall cisterns — these are built into the wall cavity and are generally not suitable for Blop, as there's no accessible space to place or retrieve the product.
High-level cisterns — the older style mounted high on the wall with a pull chain. These are not suitable for Blop. Even if there's enough internal space, the height makes it impractical to place and replace Blop regularly. Every replacement would mean reaching up to access the cistern, which is awkward at best.
Single-flush and dual-flush cisterns — both work fine with Blop. The flush mechanism type doesn't affect compatibility, as long as there's enough room inside.
The One Thing That Actually Matters: Space
Whether your cistern is compatible comes down to one practical question: is there enough room inside to place Blop upright, flat on the bottom, and away from the water inlet and moving parts?
Blop needs to:
✅ Stand upright (not tilted or on its side)
✅ Sit flat on the floor of the cistern
✅ Be fully submerged when the cistern fills
✅ Have clear space above it, without hoses or fittings pushing against it
If any of these conditions can't be met, Blop may deplete significantly faster than expected. When Blop is tilted, the gel can release unevenly and at a higher rate, shortening its lifespan considerably.
For more detail on why placement matters so much, it's worth reading: Is Your Blop Set Up Correctly?
The Case of the Old Caroma Slimline
We recently heard from a customer using an older Caroma slimline dual flush toilet. This is a style that was common in Australian homes from the 1980s through to the early 2000s — recognisable by its low-profile lid, compact footprint, and relatively shallow internal tank depth.
The issue isn't the flush mechanism or the water chemistry. It's space — or the lack of it. These older slimline cisterns are packed with internal components: the inlet valve, the flush mechanism, the float arm, and associated fittings. Together, they fill most of the available floor area inside the tank. There simply isn't a clear, open spot to place Blop upright and leave it undisturbed.
Even if you manage to fit it in, Blop is likely to end up wedged at an angle against one of the internal components, which causes the gel to release unevenly and much faster than normal.
If you have one of these cisterns, you can certainly try Blop — but just be aware that the lifespan may be shorter than the advertised estimate. A simple check before you start: open the lid, look inside, and see whether Blop can sit fully upright and comfortably clear of any internal fittings. If it's a tight fit, that's your answer.
What About Concealed Cisterns?
In-wall or concealed cisterns — the type hidden inside the wall cavity with only a flush plate visible — are generally not suitable for Blop. These cisterns aren't designed to be accessed regularly, and there's typically no practical way to place or remove Blop without a service access panel.
If you're not sure whether your toilet has a concealed cistern, the giveaway is that there's no visible tank at all — just the bowl and a flush button or plate mounted on the wall or tiles.
How to Check If Your Cistern Is Compatible
If you're unsure, here's a simple process:
- Lift the cistern lid and take a look inside
- Check whether Blop (roughly the size of a small pear) can sit upright on the floor of the cistern
- Make sure it can sit away from the water inlet hose and any moving parts
- Check that nothing above it (like the inlet hose running across the middle) would push it sideways once the lid is closed
If the answer to all of these is yes, you're good to go.
If you're not sure, feel free to send us a photo of your open cistern at crap@blop.today and we'll give you an honest answer before you open a Blop.
In Summary
- Blop works with the large majority of Australian toilet cisterns
- The main requirement is enough internal space to sit Blop upright, flat, and away from moving parts
- Older slimline cisterns (such as certain Caroma models from earlier decades) may have limited internal space, which can shorten Blop's lifespan
- Concealed/in-wall cisterns are generally not compatible
- When in doubt, open the lid and check — or send us a photo and we'll help you figure it out