overflow gurgling?

the Drain system he is referring to is known as the herbie drain system...

however to properly implement this type of drain system you need an overflow box, your drains seem to be part of the display, though that will work, the efficiency of skimming the waters surface will be next to nothing...an over flow box ensures you are only taking the water off the surface of the tank (the part of the tank where all the protiens gather..)

however the previous poster correctly described the drain setup, you need a gate valve on the main siphon drain and a gate valve on the return as well, the other drain line stays pointed up and dry with no restrictions in the line...

as for slowing your drains,LOL your draining capacity will be increased ten fold, you will have the ability to run at almost 3000GPH if you pump could supply the tank with it...(1.5" drain in full unobstructed siphon will flow ~3000GPH) by having the valve on it you will be able to control the siphon in the line and adjust the flow to match your return pump....OH YEAH, did we mention this will be dead silent???

when your drains are running in siphon there is NO air in the lines...air is what creates all the noise as the water has to fight is way down past the air...burping and boiling water noises will be completely gone running your tank with a siphon drain...

as for placing an air tube in the drain....dont waste your time, it is a gimmick that isnt worth trying, as are all the other quite your drain things out there, maggie muffler, hoffer gurgle buster, stockman durso...blah blah blah...herbie or Bean are the only two ways a tank should be plumbed for drains, Bean being the preferred but herbie works well too..

 

i helped my uncle set up a tank that was very simmilar to yours and when he bought it the guy had it set up just like that with an air line about 3in into the line and it was very quiet, although he did have a ball valve on the return lines