Optimum flow rate: 100 gallons per minute. When using a specific suction you should take into account the required flow intake for the pump you will be plumbing to and also the heater. On ALL systems it is required by BISHTA standards to install 2 suctions per pump to avoid entrapment and or disembowelment.
Best to use a plumbing cleaner then pipe cement to assemble. Pipework pushes inside this part at the female end.
Assemble through the spa shell with silicone you can use a gasket instead of the silicone but not both together as this often causes the gasket to spurge out the side and would cause a leak.