Generally, tank pressure is taken off from the muffler...

You can also use case pressure...it will be greater, but muffler press. is usually sufficient.

Most mufflers have a press. fitting...what type engine are you talking about?

edit: one thing better about muff. press. is that if there is any back flow, it will have less chance of flooding the crankcase w/ raw fuel if the line is connected to the muffler.