Leaking pop up waste from bottom side

[paul alan]

Hi guys, I have just installed a pop up waste on new basin.

I have siliconed the top with the washer, and the water holds inside the basin with the waste closed but when I pop it up to release the water down the drain it leaks out from the underside of the sink where the backnut nut washer are, before the trap.

I could just silicone the back nut washer but then I would be simply trapping the water inside and that doesnt seem right.

What can I check?

Any advice massivley appreciated














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[ShaunCorbs]

Yes need to seal both sides

 

[paul alan]

Yes need to seal both sides

thanks Sean

 

[Gasmk1]

Or use one of these Basin Waste Seal Kit | Bathroom Accessories - TYDE - https://www.thomasdudley.co.uk/tyde/products/basin-waste-seal-kit/