You only have 2 of them for the fuel. The other 1 is for the charcoal canister. A clamp? If you mean a hose clamp then just use a small screw clamp but as for the bog ring on the pump you will need it to lock the pump in.
Do All 3 Fuel Lines Pump Fuel In A 1998 Chevy Blazer S-10? How To Put On A Fuel Pump?
No , only two will go to fuel pump, the other one is for the vapor system. to replace fuel pump you will have drop fuel tank, very carefully, try to empty as much gas as you can to make easy on you.