manbeast
Aquarium Advice FINatic
One method is drilling a 1/4 inch hole in the top of the 90 degree elbow and insert some tubing airline works but I prefer the more rigid poly tubing such as the type used on rodi units, you would work the tubing in and out until you find the "sweet spot" where the tubing allows air pocket that is trapped trying to rise back up the main pipe to escape out the 1/4 inch tube, I've used similar methods before with fair results, I'd say it helps minimize but probably not eliminate the gurgling, hope this helps and hope my description comes across ok