The tub is 12 gallons, and the drill bit was somewhat undersized. I really didn't care what size it was because after I drilled it, I tapped each hole with a 10-32 tap. Since I was only running thru PVC, the predirlled hole size really didn't make much difference. If I do another, I won't bother to tap, I'll just under-drill the hole slightly. Since both pieces are plastic, they screw together fine without the threads. No sealant was needed at all. Besides if it leaks a drop, what does it matter? It's just going to drip back down into the reservoir anyway. Hope this helps.