if you put pieces on top of other pieces it takes a lot longer than placing the piece somewhere else, thus It is worth loosing a few points if the pipes are left over to allow you to get through the pipes quicker, since time is so critical.
It is good on the levels with Hot and Cold to finish one pipe quickly (a strait run) and then spend the time to make the other pipe very long,
It is good to put all the wide pipes in the begining, while you can build loops twords the end of the pipe.
just some other quick tips,
monty
