How to determine where under sink waste pipe is leaking?

[nonsibicunctis]

Hi, I have an Oliveri single sink & drainer about 20+ years old but still in reasonable condition.

After having to have my entire ceramic drain to sewer replaced recently, I discovered that there was a leak under the sink..

I dismantled the sink waste from sink to the outlet into the floor.

I discovered that the washer between the waste outlet top flange and the sink top was worn and broken so assumed that was the problem.

I replaced the whole outlet and basket with a new third party one from Bunnings which appeared to fit well.

I also cleaned out, checked the pvc (?) pipes and traps for damage and replaced the gaskets (?) on each of the waste traps to the floor outlet.

I then refitted and tightened everything.

...  There is still a leak, though less than before and despite checking that all connectors are tight, it remains.

...  As hard as I've looked, as well as drying everything then filling the sink and emptying it, I can't see or feel where the water is exiting but the bucket I've placed underneath - dry at first - I find with considerable water in it.

So, apart from calling a plumber and having to pay an exorbitant fee to get it sorted, my question is:

*** Is there  a colouring agent or something I can put in the drain water to leave an obvious mark where the water is leaking?

... Or can anyone suggest another way to discover the leak?

Undersink pipes - original was verticle but changed after addingsink from top with new waste & basket

[JacobZ]

Hi @nonsibicunctis,

Thank you for your question.

I'd suggest you put the plug in, fill the sink up and put some blue food colouring in the water, then allow it to drain while watching the plumbing on the underside of the sink. This will make it much easier to spot where the leak is coming from.

Pay close attention to all the different joins, including the spigot that dishwasher outlet hoses are often attached to.

Once we know where it is, I'm happy to assist further.

Jacob

[nonsibicunctis]

Jacob,

Many thanks for your response.  Where would I get the food colouring - a supermarket or ?

Take care. Stay safe.

[JacobZ]

Hi @nonsibicunctis,

Yes, a supermarket will carry food colouring that you can use.

Jacob