No gas-tight seal on Speidel 30L fermenter

[PHB2234]

I use a Speidel 30L plastic fermenter. I use the MoreBeer thermowell on the top rather than the large Speidel airlock. That adapter has a hole that accepts a grommet for use with the common 3/8" plastic airlock. This allows me to monitor the fermentation temperature with my Ranco ETC and a probe. I use the white, flat O-ring from the Speidel along with the Speidel locking ring. The O-ring is fitted between the thermowell adapter and the top of the fermenter, with the locking ring tightened down on top. The last few batches I haven't been able to get a gas-tight seal, evidenced by a total lack of bubbles through the airlock. Fermentation has definitely occurred, as evidenced by a temperature rise and fall as the yeast do their thing.

Is anyone else using a similar set up? How do you effect a gas-tight seal?

 

[Craigerrr]

I use to have speidels, this is how had the thermowell installed.

 

[PHB2234]

Nice photo. Thanks for helping me think of alternatives. That's a very happy fermentation in your photo!

 

[Craigerrr]

Nice photo. Thanks for helping me think of alternatives. That's a very happy fermentation in your photo!

Had to dig for that photo, that is probably 4 years ago!