On Sun, 25 Oct 2020 04:36:48 -0700 (PDT), Mathew Newton wrote:

I've got a new stainless steel Franke sink and waste, which came
supplied with sealing washers top and bottom. The instructions make no
mention of using any silicone in addition to the washers but should I
for belt and braces?

What are the washers made of and how soft are they? If they are some
form of thin (1 mm ish) soft rubber they'll do the job "dry" and
without needing to be murdered up. If they are fairly regid plastic
they'll probably need a sealant but I wouldn't use silicone, just
plumbers mait.

I'm also loath to use a washer on the top between the waste flange
and sink as the washer thickess can create a ridge that holds
water/muck. Really depends how well the flange matches and sits in
the sink. Without a washer I'd seal with plumbers mait.

--
Cheers
Dave.