4.5" fermenter lid?

So, I bought a groovy 2.5 gallon glass jar a few months back that I've been using sporadically for experimental fermenting of small batches. See below.
View attachment ImageUploadedByHome Brew1465608775.156217.jpg

I simply drilled a hole in the cheap metal lid that came with it and have been using a bucket grommet to mount an airlock. I don't feel like this has been giving me a very good seal...

What I'd like is a lid with a rubber seal and an airlock hole that will seal this bad boy up night and tight. I measured the opening and it is 4.5" on the OD of the jars opening. I'm not sure if that's a typical 1-gallon jar size, or something different.

Anyone know of something like this?

Thanks!

 

You might try several wraps around the jar's threads with Teflon tape.

 

Or perhaps try wrapping saran wrap around the screwed on lid and rim to try and create another barrier.

I would start with filling the jar with some water and dropping in a few alka seltzer tabs (or vinegar and baking soda) to create an effervescent mixture.
Quickly screw on your lid and put your thumb on the stopper hole you have and try and listen for any leaking gasses (should be able to feel the pressure building inside)

If you determine that you have a leak but cant seem to pinpoint it, you can spray some soapy water all around and it will make bubbles where the leak is (like finding a hole in a tire)