[Stevie]

Was the cap dry? I have silicone bungs that pop out under the slightest pressure if they are wet. I sanitize and allow them to dry under cover.

[Philbrew]

I love my Big Mouth bubblers. I have never had an issue. I have the 6.5 gallon with the spigot. I use a 3 piece airlock.

The lid pops off under pressure too easily.

A brick on top alongside the airlock fixes that problem.

[ynotbrusum]

I think the glass Big Mouth Bubblers are the ones with the pop off problem - I specifically bought the new lids with the silicone, because the original screw on lid did not fully seal well on my plastic version.  The silicone collar on the press on lid holds the seal well.  YMMV it seems.  I like the easy cleaning access that the wide mouth opening allows.

[el_capitan]

I have both models of the glass Big Mouth fermenters.  I haven't had any issues with the seal on the old screw-top model, and I'm still using the original foam gasket.  I guess maybe I got lucky there.

The newer fermenter is a better piece of equipment IMO - The glass is much thicker and there are volume gradations.  The cap is kind of weird though.  I think the key is to line it up really straight-on to be sure the silicone ribs go in straight and evenly.  If you cram it in there off-kilter, it will want to pop back out.

If you be sure to use a fermenter with plenty of extra headspace, and try to ferment at a cooler temperature (65-70 degrees) you should have no problems in the future. 

Welcome to brewing!

[ultravista]

I have the new BMB with the older lid. I use two gaskets in the lid and it seals easily.