Why complicate your life?
T'ing it into a cockpit drain requires an expensive bronze barbed T fitting (as its potentially below the waterline) + an expensive vented loop, that must either be maintained annually (basically just unscrew and wash out the rubber air inlet valve - but access will be a stone bitch) or have its own vent hose and vent fitting.
It adds three extra joints to the drain to increase the risk and also, if the reason you are running the pump is a split cockpit drain, shutting the seacock will stop you getting rid of the water!
Well above the waterline with a simple plastic through hull with no seacock is cheap, doesn't compromise the cockpit drains and will give you better flow than anything that has multiple joints or fittings in the hose.
My JR Contessa 26 has three 1/2" cockpit drains to the bilge (non-self draining cockpit) and a 1 1/2" drain straight out through the transom from about 6" up the rear of the cockpit with a non-return valve, that is supposed to help if you get pooped. There is not really enough room to fit a seacock + the angle is virtually impossible and access to operate would involve relocating the gas locker, but as the drain is well glassed in 2" copper pipe up to the valve, I don't worry much. Unfortunately wave action 'burps' the valve and if there is any fine floating debris or even weed about, it can jam the valve open so I keep an expanding rubber dinghy bung in the cockpit end through hull fitting except in heavy weather.
Cockpit drain seacocks are GOOD, but its use them or loose them. If you dont operate them weekly or at least whenever you go to the boat, they are likely to be seized when you most need them. You also should have a good supply of tapered bungs easily accessible or even taped to the hoses in question. Bungs should be chosen to have a small end that suits the fitting and a large end that will still adequately block the hole if the whole fitting has sheered off and the flange dropped out. Tied on with a lanyard is a PITA as it is one more thing you have to undo if the lanyard is short, and if its long the bung is likely to have floated off somewhere awkward and jammed out of reach. Give me a couple of turns of tape you can twist loose any day!