Sink strainer wastes without foam washers

[faddy74]

Replacing the knackered strainer waste in my son's sink, the old one had a rubber seal under the sink and a foam washer above. Bought two from Screwfix to try, (one Opella, one unbranded) and neither have a foam washer. Should they have come with foam washers (neither have instructions)? Whichever one I fit, should I reuse the foam washer, use silicone, or fit it without either?

 

[dpsservices]

Me myself smear of silicon
Regards david

 

[Madrab]

The 90mm wastes usually have such a large washer underneath now that they don't need a washer under the inside sink waste anymore. As @dpsservices though, I'd usually use a little dab of clear silicone none the less as a belt 'n' braces.

 

[Hot&Cold]

Just fitted a kitchen sink (not screwfix) which included 2 very thin foam gaskets.

The sink instructions said use silicone on uneven flange surfaces but there is no uneven surface,i take it's a hint to use silicone.

reuse the existing foam washer, dry it out and apply a continous bead of good quality clear silicone to the sink flange and same to the strainer flange,sandwich in the foam gasket. Bolt it together and leave any excess silicone to start curing. Last part of the job is to trim the excess silicone with a stanley knife.

 

[John D v2.0]

No need, both sides of that connection are"inside" the waste system so there's no need to prevent leaks through.
The seal is underneath where you say you have a washer anyway. The top is just a mechanical connection to hold it in place and look nice.