By Mary in PA on 3/3/2011
My experience agrees with the other posters above. We put in our septic and are planning to build the house this summer. I did it then, because we had the money, it got one more thing off the list before the "big event," and the excavator was on site for other work at the time. Depending on when you build (in our area) if the house is nearing finish and you get a real patch of wet (40 in. of rain/yr. here) it can delay putting in the septic for a while, which can delay getting a C.O. In terms of planning, we had done some fairly in-depth site planning on our own, and based the work on that effort. We have a large tract, so precise placement is not critical.
I had the well put in a few weeks before the septic. In my area, occasionally they have to move from the original drill site if water is stingy. So while I can't claim ultra foresight in planning, I was glad to get the well in first so that I knew I had more than code distance downhill to the planned septic site. By the way, we drilled the well but have not yet installed a pump.
The septic is about 100' from the house and sits between (and is shared) by two buildings - the future house and the shop we put up last summer. When it was put in, we connected it to the main waste pipe for the existing shop. The other stub from the septic will be brought the ~150' up to the house after we excavate for the basement and start plumbing rough-in.
A note on septic size; we sized our septic system for a five-bed house, even though our plan shows three bedrooms. The actual cost for the system and install were not that much more for a larger system, and in our area it is extremely difficult to alter septic system size at a later date - if someone were to want to add onto the house, for example. So that is something you might want to consider.