i put small valves on my airline tubing to adjust how much air goes in , works every time, so instead of restricting the drain itself to make it quiet which is a bad idea if you dont have an emergency you restrict the air , the less air the faster it drains your overflow box(put your finger and block your durso it drains the b ox fast untill air starts to get taken in and make horrible noises) the more air you allow in the slower you make the drain.
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