My kitchen and bathroom copper pipes all have some green stuff on them. It's a 15 year old house. but there is no obvious sign of leaks. should I be concerned? what can I do to clean it off?

I'm assembling a new two-handle lever-style lavatory faucet and the Y fitting (joins hot and cold lines to spout) has a rubber washer inside of it. Do I need to use teflon tape on the adjoining spout threads? I already had to disassemble this connection once because it was leaking, but found that the rubber washer had pushed its way up inside the spout because I evidently over tightened it. Mysterious thing is that I only hand tightened it and gave it maybe another half turn with a wrench. I'm tempted to remove the rubber washer and just use tape. Is this a bad idea?