[Gaffer]

My B-I-L is retired now but owned a plumbing company for decades - a wealthy man.

He always said there are only two things you need to know about being a plumber:

1. Sh!t flows downhill, and

2: Do NOT bite your fingernails!

[central_va]

I always thought there were 3 things a plumber needs to know:

1. Hot on left, cold on right
2. Crap runs down hill
3. Payday is on friday

[T-Bird45]

Good rules — I heard there were 3 Rules for a Successful Plumbing Career:

1. Sh!t flows downhill.

2. Wash your hands before dinner.

3. Payday is Friday.