Sealing replacement basin waste - silicone residue

[chris1982]

I need to fit a new waste to a basin after removing an old one that was fitted (poorly) with silicone. I removed all lumpy bits of silicone and most of the the finer bits with silicone remover, but there is still some silicone bits left that I can't get out.
What are my best options for getting the new (slotted) waste watertight? I bought a basin mate kit as well as plumbers mait (and got a big washer for it), and got sanitary silicone as well.
Or to put it differently, what is better when the basin hole is a bit uneven?
P.S.: Accessing the backnut is a bit difficult.

 

[foxhole]

Have never used silicon to fit a waste, just a bit of plumbers mate and well fitted washer.(silicon eater available for cleaning)

 

[chris1982]

Plumbers mait above and below the basin, or just below?

 

[foxhole]

Both

 

[Madrab]

Have never used plumber mate, horrible stuff IMO, sticks to everything.

How I fit .... Nothing needed on the inside of the basin, just the thin washer ... centre the waste, fill the gap between the shank and the basin and a little down onto the shoulder, hold the waste centered and fit the washer and nut (aligning the slot), and tighten by hand then one full turn with adjustable piers, run finger around to tidy up extruded silicone, use what's on your finger to run around the bottom of the nut at the threads.

 

[chris1982]

Lots of different techniques. I still wonder which one is best when replacing something that was siliconed in.

 

[Madrab]

Lots of different techniques. I still wonder which one is best when replacing something that was siliconed in.

Whichever is preferred.

If the previous one was siliconed/mated/othered in then all the previous material should be removed, so in essence you would be starting with a new basin surface.

 

[keen2learn]

Have you considered a basin mate, cheap and perfect seal, aimed at diy I’ve used myself worked perfectly.

 

[chris1982]

Thanks basin mate was on my original list anyway.

I just installed it with basin mate and extra silicone as Madrab described. Will wait until tomorrow morning for testing.

 

[chris1982]

Turns out it's weeping! When closed, it holds water in the basin, so at the top it's tight. But when the waste is open, it weeps around the backnut.
Thinking about it, I might have put too little silicone around the threads where the conical washer ended up, though the basin mate guidelines claim no silicone was needed.

 

[HERTS P&D]

Tighten it up a bit more.

Andy

 

[dilalio]

Removal of existing silicone is 1 of the reasons I use mait.
Another is that you can test the basin immediately after fitting.

 

[HERTS P&D]

Yes, I fit and test them straight away, I don't want to wait for a customer to call me 24hrs later to let me know there is a leak.

Any work I carry out is shown, explained and tested in front of the customer before leaving site.

Andy

 

[Madrab]

If using a basin mate then it needs to be tightened enough to be squeezed up into the gap around the shank of the waste, doing that should press it into the threads sealing them up. Normally shouldn't need anything else when using a mate.

+2 with the testing once it's all together, if it's going to leak it'll leak then.

 

[chris1982]

Thanks all. I removed the silicone around the bottom of the basin mate washer and managed to tighten the backnut a tiny bit more (1/6th turn perhaps). Now it looks like this and the waste seems to be water tight.
For piece of mind is there anywhere I should add some extra silicone below the basin mate?

And I discovered that most of the leakage was from the U bend of the waste pipe I screwed on poorly... At least that is more straightforward to re-do (or so I thought)...