I needed one of these couplers that absolutely would not leak, even under CO2 pressure. I read review after review on various brands that were generally positive but all generally leaked at least a little (duck tape does NOT hold up when the water source is under the adhesive). The was the only one that had no reviews that mentioned leaking, but only one review that had just made the step up from pure duck tape, so obviously, no contest there.
Will this brand work with no leaks? Honestly I didn't even give it a chance by itself, but the inside thread is perfect for what I had in mind:
While I was waiting for this to arrive in the mail, I went to a local hardware store and for about $1, I bought a small pack of flat, rubber, garden-hose washers and put one in each end of this coupler. Then, I removed the white plastic rings from the neck of both 2-litter bottles (the ring that's left over from the cap), I added the liquids, and screwed both bottles in.
The result was perfect, even when the liquids were carbonated. The rim of each bottle screwed into the rubber washers, making a perfect seal, and the rim of the coupler lined up perfectly with the collar of each 2-litter bottle.