Anotherpop up waste installation question

22 Oct 2010
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United Kingdom
I bought an ex display vanity unit/basin/taps/popup waste at the builders merchant and it didn't have a washer for under the basin. So i bought from them a plastic washer, fitted the whole thing and it leaked. Went on t'internet and numerous people say discard the washers and use silicone. The lip of the screw in part of the waste is very narrow and the basin hole is quite big so i tried using silicone and the plastic washer. That also didn't work. (bearing in mind the whole thing is assembeled so i'm working from underneath now.)
Then i thought - I keep reading about a rubber washer but what I'm using is plastic.

Question1. should it be a rubber washer and would that be likely to work better than the plastic one.
Question2. is it best to use washer and silicone or washer alone or silicone alone
Question3. I'm wary of not using a washer as i don't want to crack the sink glaze - is that an irrational fear
Question4. If I just use silicon and no washer how much should i use and how tight should I tighten the bottom part

Many thanks for help
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it's a pop-up waste, they all leak.

buy a plug.
Use rubber washer/silicone.
The silicone seals water from passing the thread.
Ok - looks like a trip to bandq tomorrow to see if they have a rubber washer
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No reason your plastic washer should leak.
Have you sealed the bottom properly with silicone. ?
Well I put silicone on both surfaces of the washer - obviously most of it squeezed out!
You need to seal the gap between thread and basin with silicone, then fit washer/nut.
Doh - easter sunday tomorrow - bandq closed!
Thanks seco - maybe this is where i'm going wrong - I'm using silicone on the washer but not sealing the (considerably wide) gap between the basin and and the thread
Yes seal the gap.
If you look at the waste water don't just run down the inside it also runs down the outside due to the 2 slots and the overflow design in the basin .
So you need to seal the gap or the water seeps through the thread and out the nut etc.
Ok i'll be onto that tomorrow. I'd just assumed that a combination of ptf on the thread and the tightness of the connection with the washer would be enough.
I'm using some Dow Corning sanitary ware sealant that i picked up from the builders merchant. If I use a decent chunk of it (like i have for the top part of the waste) it doesn't seem to have fully gone off after 36 hours (the surface has but not deeper in - any thoughts?
I'm using some Dow Corning sanitary ware sealant
Whats that 785 (clear) ?

If I use a decent chunk of it (like i have for the top part of the waste) it doesn't seem to have fully gone off after 36 hours (the surface has but not deeper in - any thoughts?

What you have used it under the lip of the waste in the basin ?
It does take a while to go off but i've tested and used wastes before going home from jobs and it's been ok and never called back. ;)
Oh and another question occurs - do i seal it, let it go off and then fit the lower part with washer etc or do it all in one go - I'm just thinking that doing it in two stages means you lose the ability to adjust tyhe positioning of the top part to make the pop up assembly go in the right place.
Just run a bead of silicone round smear with finger so gap is filled and whack washer/nut straight on.

Time you have tidied up your tools etc the basin willbe fit to use. ;)
Ok done that - will wait till the morning and see what happens! Hopefully will be able to report back that all is in order!

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