Sealing a bung in a pipe for a pressure test?

[Weebles]

I have a 100mm bung to seal into a 110mm pipe to pressure test my drain. Can’t get a good seal. Get leakage around the edge. What should I use to make a good seal? Thanks

[Temp]

The pressure for the test is usually quite low. To temporarily seal one 50mm pipe I tapped a poly bag over the end.

Edited September 18, 2019 by Temp

[ProDave]

Is this a new bung or an old one?

 

If old the rubber may have hardened.

 

Try smearing vasseline around all mating surfaces to help make an air tight seal.

[Weebles]

It was a new bung.  But one of the plastic ones not a metal one. I had a go with the vaseline but couldn't get the Horobin air test thing to work at all.  Pressure dropped slowly but too much over about 3 minutes thus suggesting a leak somewhere.  And this was in a test pipe with no joints!

However, at the suggestion of our tiler we bunged the end of the 110mm pipe (this time with a far more solid metal bung) where it joined the manhole, tightened it good and proper, filled the entire system up from the inspection chambers until the water level was above all the pipes and joints, and then left it for a few hours.  Minimal fall in water level (some evaporation on a hot day possibly) so we are happy that our drains are all good.  Took some photos for the building inspector in case he ever asks.  Some local builders across the road maintain they have never done a drain test using air testing in 20 years of building new houses.....  

A bit unconventional in the end but we feel confident enough to back fill now.

[Oz07]

I always water test. Bit of a luddite but you know what you know. Just remember to put some longer stubs on when doing as your supposed to create 1m of head. I don't think I've ever had an all plastic system lose any water yet. Pretty much foolproof. Even those flex seal couplers are pretty much 100%