Gurgling sound on intake bulkhead

[mark]

Looks like you just have a up turned fitting and it will be noisy. Single line solutions like Dursos, Stockmans and Hofers always see in a overflow box, not sure if will work without.

Few threads over on RC where people have gone without a overflow box and from a bulkhead similar to how you are drilled ran a horizontal piece of PVC along the back wall with a slit in it.

Herbie is one of the quietest since as Eb0la11 said no air (like Dursos, Stockmans and Hofers), to do one you'll need a second drilled hole. See Reefjunkies Herbie (here) where the holes are stacked.