I use the spaflex in drain. They dont really bend 90 degress, i guess you can say they curve, it is also heavier than pvc so you have to support it if you have your drain at the back of tank instead of under it. Or the weight of it will cause the bulkhead rubber seal to shrink unevenly causeing very slow leak over time.
For noise i had straight pvc plumbing in a pump, im using an insump pump not external, theres so much vibrating noise even after putting pump on rubber or styro mat. I have to redo my return eventually to lessen the noise. Straight lines for return avoid 90 deg bends
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