On Sunday, 25 October 2020 at 20:02:38 UTC, Mathew Newton wrote:

I must admit everything does feel like it is good quality, and whilst I do tend to do belt and braces (read: over engineer everything) my gut feeling it it really isn't necessary on this occasion. I could always dry-fit and only deviate if the need arises.

I should've uploaded a picture really as thinking about this it has dawned on me that not all sink wastes are the same.

Here's what I've got:

http://www.newtonnet.co.uk/permanent...esinkwaste.jpg

With the above-sink parts consisting only of a pressed plate (i.e. there's no threaded column that protrudes through the sink hole) it's clear that the watertight seal is actually a function of the rubber washer *underneath* the sink. If I was going to be putting silicone/PM anywhere that's where I'd be needing to put it but given the ridges on the washer I don't think it'll be required.