Recessed drain fitting

Hi folks,

Thought I’d share my latest project: recessing the drain on my water table. I was originally planning to silver solder the brass fitting to the underside, but someone on the forums suggested a “flat recessed” dimple die. I don’t have access to tooling like that, or a hydraulic press for that matter… so I cut some parts on the Crossfire and knocked this out with a long wrench. I’m chuffed as chips with it!



I simply used a 1/2" PVC flange from below, sealed with some 3M 5200 and four SS 1/4" bolts.


This is really weird. I don’t think I’ve ever seen a PVC flange before! I DAGS it and, sure enough, they exist. Never saw one in a HDW or Plumbing supply store though. Fascinating what you can learn on the web!

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I once managed a Household Chemical ( dish washing liquid, laundry detergent, etc.) factory across the street from my house. During their start-up, they did not have the funds to purchase SS tanks and plumbing. I Used Polypropylene water tanks to build their mixing and holding tanks and 2" PVC plumbing all the way. Those PVC flanges were a Godsend! Now they have big 45,000L SS Mixing tanks (Designed and built by me) with 20HP motors. Also, a really nice PC Networked (Modbus) monotoring and control system which I also designed and built. Sorry, off topic!:rofl:


Excellent. For some reason I didn’t think this would work, like I’d have to use some magical Steel to make a simple die, not sure why I thought that.

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For a few jobs normal steel will hold up fine (so for 90% of us here). If you plan on making dimples 8-16 hrs a day 7 days a week making them out of tool steel makes sense.


I got a PVC flange for my table but am uncertain about two things:
First, the inside face of the flange isn’t totally flat, it’s raised slightly in the center (which might be ok if that is used to center the flange in the hole), but the mounting holes are also raised, which, I would think would create a potential for leaks. I guess it depends on how ‘goopy’ the 3M 5200 is. I haven’t used it before, but I did get a tube for this application.

Secondly, the mounting holes are HUGE! They’re 5/8" diameter! How do you use a 1/4 bolt in this???
I’m thinking that I need to make a backing ring that the screws thread into to pull the flange tight to the bottom of the water table and that I should put the flange on my lathe and turn off the raised face, at least the raised port around the mounting holes.

What’s your advice, master of flanges?

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you need to use a rubber gasket between the top of the flange and bottom of the table.

something like this. you just gotta cut the holes out. it’ll create a goos seal when you tighten the bolts down.


this is how did mine.

look a few more posts down and i show the top of the water table with the bolts installed… I used some of the silicone that came with the water table in between the top of the table and bottom of each washer to create a goos seal… hasn’t leaked since.


Cool! Thanks. So, what size bolts did you use? Were the mounting holes in your flange as large as mine?

I’ve got some sheets of butyl rubber I can use. I like using that because it’s safe and easy to cut on my laser cutter.

i think i used either 3/8 or 5/16 bolts and washers. the holes on the flange were 1/2" i believe and the center hole was 1’’ threaded. i enlarged the drain holes on the water table to about 1 1/4" with a step drill bit.

I’ve already enlarged the hole for the Drain Bushing I currently have installed (used the Plasma cutter to cut the hole :slight_smile:

I think the gaskets are a good suggestion and I’ve got some nice SS Truss head bolts for the top side. I’ll cut a ring that backs up the underside of the flange. Or… I’ll just keep what I have which already drains pretty well and move on to something more interesting.

Thanks again for your help. I appreciate it.

Ok, I did not use any rubber gasket just liberal amounts of 5200. As for the HUGE holes, I made aluminum “top-hat” Bushings with 1/4" holes in them on my lathe. I use SS 1/4 x 2" Carriage bolts to secure the whole thing to the water-table. 5200 on everything, bushings, holes, bolts, everything!
No leaks, works great!

I double stacked gaskets on my flanges, then used flange bolts with rubber washers inside the table and flange nuts underneath. No leaks or anything. I was wishing I had made the simple die, but I just found a great filter for the 1inch PVC I used and I’m pretty happy with it now.

Initially I made gaskets from some .134 thick rubber but when I got it in my hands I realized it was not a good idea. When I put the gasket and flange together face down on my surface plat the center section had a lot of wiggle in it.
The step is .083. Using my gasket defeated the design of the plastic flange assembly. It’s meant for the flange to pull the center portion tight to a mounting surface, unless the rubber is soft enough to allow the parts to come in contact. Using a gasket thicker than .08 will keep the center from meeting the mounting surface when tightened.
Making up the difference with calk may very well work, but in theory leaves the door open to failure later on. Maybe when the calk cures it will work just fine. I don’t know. Just say’en.
I suspect the .080 space might put excessive stress on the flange, so I’m making a .063 alum spacer leaving .020 of tightening space, enough to pull the center tight to the underside of the pan and reduce the stresses on the outer flange. This way there is no wiggle room between the sealing part of the flange assembly and the water pan eliminating the reliance on the calking to keep it water sealed. I will still use calk to compensate for irregularity between mating surfaces and the gap around the two parts of the flange assembly.