Top tip for plumbing: If you’re connecting two pieces of pipe together use push-in connectors (like this, for example). No soldering, you can take them apart when you make a mistake (not if), and they don’t leak.
By contrast if you need a mechanical piece, like a washing machine connector or valve, choose brass fittings (like this). Plastic is too fragile to keep working if you’re going to be fiddling with it, so the extra hassle of having to tighten up the connectors to the right level is worth it. And while you’re there pick up some extra olives to go inside the brass connector; you’ll thank me when you make a mistake (not if).