"When buying male fittings, it’s best to always get tapered ones so they fit in either."
I tried that with a shop compressed air system and got lot of leaks, hissing, and the compressor turning on frequently. And I never did get the system not to hiss somewhere, so I can sympathize and ditto this rant. Even when using matching fittings, with gobs of tape and/or dope, and enough force to destroy multiple fittings, it leaks. I'd pay a plumber well to teach me some of those mystic arts, if I could find one in my plumber-free rural area.
If you're talking about quick connects, they'll always leak a bit.
The threaded fittings however are a different story. Assuming you didn't use stainless steel on stainless steel fittings [0]:
* You can find the leaks by spraying soapy water on suspect connections and looking for bubbles (wash off and dry with clean water afterwards unless you want some serious corrosion). You can also buy a jar of noncorrosive propylene glycol based leak check fluid at your local hardware store for somewhere around $10, which is a strictly better option although it's a bit harder to clean off.
* Undo the connection and throw away every fitting you can replace (you generally should not reuse NPT threaded connections unless you know what you're doing). Clean all fittings until they look brand new and with no visible debris on/in the threads.
* Watch some videos [1] and remake the connection using the proper amount of tape and sealant and appropriate torque [2]. Only tighten the fitting. If you loosen it even a bit during the process, undo it completely. Clean both sides, reapply tape and dope, and try again. Let the sealant set ~24h and retest.
[0]: Stainless steel pipe connections are a special case because they tend to cold weld before they're fully tightened. There are ways to mitigate that but the short answer is don't use them if you don't already know how.
[2]: NPT connections really shouldn't be torqued (you instead use turns from hand-tight for properly cut threads) but if you're having trouble find a torque chart for your fitting material (copper, brass, steel, etc) and follow that.
I tried that with a shop compressed air system and got lot of leaks, hissing, and the compressor turning on frequently. And I never did get the system not to hiss somewhere, so I can sympathize and ditto this rant. Even when using matching fittings, with gobs of tape and/or dope, and enough force to destroy multiple fittings, it leaks. I'd pay a plumber well to teach me some of those mystic arts, if I could find one in my plumber-free rural area.