another loud drain. plastic gate valve?

[damtrees420]

So i bought this tank with two 1.5 inch drains drilled on the back about 4 inch from the top so i set up the drain with just sticking a 90 in the bulkhead and another 90 on the outside i knew it was going to be a long shot but it is loud as hell running about 1800 gph through the two drains does anyone know how to better run them keeping in mind there is no over flow the drains are right in the tank with just a 90 and about an inch of piping have seen people put a t on the outside of the tank to the bulkhead will that help brake it trying to siphon ? any help or ideas would be sweet as would love to button it up as this is the last thing keeping up the progress