use a grommet?

[drunknbass]

im building a flood/drain table and was gonna buy a kit of the tub and had a question about these,


do i just tighten this down(on the tub) really tight, or use a silicone gel to seal it, or maybe a grommet?

 

[Legallyflying]

That is called a bulkhead. You unscrew them and install it in the hole..the rubber washer goes on the "wet" side of the table. When you tighten it down it will clamp tight and seal. no need for silicone or anything.
cheers.