and sometimes those shouldn't be very tight at all. This counterintuitive bit of secret knowledge might be the result of the sheer weirdness of plumbing fittings in general. Spend a few moments ...

copper tee. If you have CPVC (plastic) or steel pipes, add tee fittings made of the same material. If you don’t want to solder, you can cut the copper water pipe and install a 5/8-in.