First to all, thank you for the replies and sorry for the delay in responding. I hadn't intended to disappear for days (and days) but life and other projects kept me busy.
There is a tool called a "tile probe". Septic guys, tile contractors, excavation contractors that install much underground piping, etc. have and use these.
It's nothing more than a stiff metal rod with a tee handle on the top pushing end and a ball bearing welded to the bottom probe end. You shove this tool down into the earth to locate pipes by feel. You can't use them in some really hard soils and rocks can confuse you, but they do work. If you know a for sure location of any of the buried pipe, start there, then keep probing and follow the pipe, marking the surface of the ground as you locate it.
Thanks for the tip. I used something similar to locate and dig out the septic lid for pumping a few years back (I wasn't going to pay for that). Only I used a large piece of rebar (and had a good idea where the lid was)
I do not think it will work for a larger project, as you point out rocky soil can be a problem; I know in my yard the septic tank top is 2.5+ feet deep, the fill above it contains softball sized rocks, the rest of the yard ... well Maine "grow" rocks every year new rocks appear at the surface thanks to freeze thaw cycles. I also have an (abandoned) concrete vault leach field and shallow ledge in one spot. I am afraid too many false positives will occur.
Sewer line cameras. Most home inspectors have them.
Could you elaborate? I have only known these to be uses to search for an obstruction/inspect pipe condition.
How do I correlate what is on the screen for the camera with what is in the yard (edit: just got to the point in the thread where you mention RF location)? Can they be "steered"? (if the RV line is real it either joins the house line a a sharp angle or has its own connection to the septic system).
It wasn't specified, but if you septic tank has an accessible cover, you may be able to shine a light down into it and see the general direction the RV pipe is heading off towards.
the lid is 2.5+ feet below ground (without a riser) and made of concrete. When I dug it up for my last septic clean out, I could not make in budge. If I dug a bigger whole perhaps I could get better body mechanics and *maybe* lift it ... I think I'll wait a couple years until the next clean out is scheduled and just ask them to take a peak.
In my area, you can call and have the underground utilities marked (for free). It picks up my sewer line. Do you have similar? Worth a try if so.
Good idea, unfortunately that will only work here if we were on public water/sewer (we are on neither). We have a similar dig safe program here, but it only marks buried public utilities. We have had them out before and they marked power/cable/phone; I know for a fact those line crossed our plumbing at at least one point, but it remained up marked.
As this is not urgent, I guess I will wait until I have the septic pumped again ... unless the rf probe seems viable.
Thanks again for the all the input.