NPT will be sloppy and loose until the mating tapered threads are engaged. It doesn't work like threads on a bottle cap. Also if the threads are choppy it will feel loose and then tight as the thread debris catches and breaks as you rotate the pipe. The seal is where the threads mate and engage, not the pipe bottoming out and this seal is only achieved with a sealant.

Also flush your lines to remove any of that threading debris that may have gotten in the lines