How to investigate a toilet leak?

[fix]

Noticed a minor leak along the grout line, coming from the base of toilet bowl. It happens after a flush, so probably unrelated to the cistern.

It's a back to wall toilet, so not much is visible from the outside. Thinking to move the toilet to check if the pan connector is loose.

Two questions come to mind:

1) There are no visible bolts, is it just silicone holding the toilet in place? Can it be undone by running a blade under?

2) Any special silicone to adhere the toilet back in place?

Thanks in advance for your input.

[MitchellMc]

It sounds like you’ve already got the right approach in mind @fix. If the leak happens after a flush, it could be coming either from the pan-to-connector seal or, if it’s a back-to-wall toilet with a separate cistern, from the seal between the cistern and pan.

For removing the pan, if there are no visible bolts, it’s likely just bedded in silicone or possibly a mortar base with silicone around the edges. You can usually cut through it with a sharp blade. An extendable blade can help if it’s a deeper bead, but take care to wear cut-resistant gloves and eye protection and cut away from your body.

Once you’ve repositioned the pan, any standard clear wet area silicone will work to re-bed it. Make sure the area is clean and dry before applying it. You don’t need anything special. Just a normal plumbing-grade silicone will hold the pan securely.

Be advised that remove and reconnecting a toilet could be considered plumbing work and might require a licensed plumber.

Please let me know if you have any questions.

Mitchell

[fix]

Thanks for responding.

Borrowed a borescope to look inside, through the unused hose inlet hole on the side, observed 2 issues.

1) The wing nuts underneath do not look like the captive type, so once the cistern bolts are removed, they will drop to the floor. They also look rusty, so would not be easy to unscrew in the first place. Which means the toilet needs to move regardless.

2) Found the leak, as you said, from the pan-to-connector seal, can see water dripping after a flush. Would the following be a suitable replacement? Is it just a direct swap, no glue or sealant required?

https://www.bunnings.com.au/holman-100mm-dwv-rubber-pan-collar_p0079198

Also, while the toilet is fully accessible, would it be a good idea to replace the cistern bolts and wing nuts? Or generally better to leave them alone for the time being?

[MitchellMc]

Hi @fix,

You’re on the right track with your observations. There are a few different types of pan collars: some look like the Holman one you linked, and others are rubber ring seals that sit inside a plastic retainer. The key is to match whatever is currently installed, both in type and size. If it’s the same size and style, it should be a direct swap with no glue or sealant needed.

While you have full access, replacing the cistern bolts and wing nuts can be a good idea, especially if they’re rusty. If they’re heavily corroded or likely to fail when you try to remove them, it’s best to replace them now to avoid trouble later. If they’re just surface-rusty but still structurally sound, you could leave them, knowing that any replacements will likely face the same long-term corrosion. Since you’ll be moving the toilet anyway, it’s usually convenient to swap them while everything is accessible.

Mitchell