No, a 3" pump will not break 4" thinwall. The bigger pipe will lessen the pressure if pipe is open. Unless you open the valve at the lower end you will not be priming the siphon due to airlock.
Most thinwall I have seen is rated for 80 PSI. In my experience, the rubber couplers will slip off at anything above 30 PSI. I have tried them. I wound up using compression couplers.
Last edited by John F; 01/12/17 11:24 AM.
