Need some advice. My fuel pump in my 69 has a fuel inlet and a fuel outlet and another fitting I think for a return line. I do not use the return, I use a single line system. So I capped it with a rubber vacuum line cap and a pinch clamp. After about 300 miles it gave out (broke, popped a hole in the end of the rubber cap) and sent gas all over. I figured it was a faulty cap and went to the parts store to get another 3/8" vacuum cap. The parts guy said that vacuum caps will hold for vacuum but not pressure. Is there a special type of cap to cover the return outlet ? The return outlet on the pump is not a screw in , it is part of the pump. I thought that these vacuum caps would work OK but its not going to be relaxing to drive until I get some good advice. Am I doing something wrong , faulty cap or faulty parts guy ?

Get a new pump with a single outlet.The rubber caps aren't meant to be in contact with gas.

Thank you. If its between the part, the parts guy or me ,it is usually me that is doing something wrong. I thought about a 1/4" fuel line with a bolt and clamps but that would be me doing something wrong again. A new fuel pump it is. Thanks again.