Here's a close-up of the lower one with silicone. This skimmer was a first shot at working with acrylic and my first shot at building a skimmer. I had no idea what made a skimmer work and what didn't so I just tried to follow pictures I had seen and stuff I had read. The first time I tried to drill a hole in the round tubing it cracked so I had to scab a scrap piece of round plastic over the crack. Honestly it looks like crap but it works like a champ.

 

And here's the upper seal. This one doesn't leak but it is really under no pressure and it was the second one I installed so it went a little smoother.

 

Sorry for all the crud in the collection cup for this picture, doesn't really show off the equipment that well.

 

 

I used them in some 55 gallon plastic drums for water storage.  Plumbed with uniseals for filling and draining.  Worked great..

 

I have used them several times to do Protein Skimmer Modifications, again, they work beautifully.

 

I have never used them when I could get a good seal with a bulkhead though.  I would always choose a bulkhead if the application works.  Good seal, room to plumb, etc..

 

But for some uses, there is nothing better than a Uniseal.

 

Dave