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What size rubber grommet do I need for a water-tight seal on a 3/4" PVC pipe?

For example, would this rubber grommet fit a 3/4" PVC Pipe?

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water tight for potable water eg high pressure or just for some sort of drain –  UNECS Dec 26 '12 at 10:05
    
Yes, knowing the usage would help. –  The Evil Greebo Dec 26 '12 at 10:52
    
No high pressure. I'm converting a 37 gallon rubbermaid container into a holder for rain water. I'm drilling a hole in it and putting in a 3/4 PVC and I need a suitable grommet that won't leak. Thanks for any advice I do appreciate it! –  stormist Dec 26 '12 at 16:28
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3 Answers 3

In these situations, I use bulkhead fittings. It saves the annoyance to getting this stuff to seal properly, any slight leverage and there's now a leak. These are available in several sizes at most plumbing supply stores. If there's a gentle curve to the surface this has to penetrate, I've used a large O-ring instead of the supplied gasket. They're available as glue type fittings, or internally threaded.

PVC Bulkhead Fitting

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Any links to one of these by any chance? I can't seem to find them on-line –  stormist Jan 4 '13 at 4:12
    
Searching for "bulkhead PVC fitting" finds dozens of places to buy. –  gregmac Feb 19 '13 at 20:47
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Schedule 40 3/4" PVC pipe has a nominal diameter of 1.050 inches. The grommet you have highlighted has a 1/2" bore or inside diameter. A grommet with a one inch bore should provide a tight seal. Just remember that water tightness also relys on a tight seal between the grommet and the container. This requires a hole as close to the shoulder diameter (not the overall diameter) as possible. As this type of container has a thin wall I would install the grommet with a generous amount of silicone sealer.

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I actually just built something similar. I tried all different types of gaskets, washers, etc. and all of them leaked under the pressure. I finally settled on a large metal washer on either side with a nut to apply pressure and liberal amounts of silicone. It's been a week so far and no leaks. The other trick is to drill the holes slightly smaller than needed. I then heated up the plastic to make it pliable and pushed the pipe through. It's helped make a nice tight seal, along with the silicone.

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You can also buy a threaded coupling that has a backing nut to accomplish the same idea as Steven but glue the PVC into the proper coupling –  UNECS Dec 27 '12 at 0:00
    
@UNECS The term is bulkhead fitting or tank bulkhead fitting. If the hole is drilled through a fairly flat area, this would be the best piece of plumbing to use. –  Fiasco Labs Dec 27 '12 at 2:27
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