Go to the Ilford website, look at the technical specifications sheet for
FP-4 under rinsing, it gives a method, for doing this as well.

W

Set up a rain barrel. No kidding.

A renounded photographer today once washed his prints on the cement ledge of
his home in France when it rained. He still has those prints. Most
excellent.

Michael

You may want to check with the local people familiar with your septic
system.  I am also on a septic, although I have city water.  Rinse
water is not a big problem for the system.  I do take some of my
exhausted chemicals down for disposal rather than dump them into the
septic (I dump developers and stop, I save fix and toner).

Although getting back to your original question, I believe that David
Vestal, in a book on B&W that he wrote, probably in the 60s, claimed
that you could rinse your prints in still water, for a long time (I
think that it was hrs) and that it would give you an archival wash.

Mark

Dan Quinn here is the "minimalist."

But essentially you can wash prints by successive changes
of water in tray as efficaciously as in a 20 gallon print
washer running a 1 gal/minute. Simply gently cycle the prints.
I don't do this but on occasion I will just soak a print
clean if it's just one print and it works well.

Also to save water some use an alkaline fix, which requires
less wash time (i.e., no thiosulfate ions to wash out.) I
use the archival fix method: Rapid fix at 1+3 for 1 minute max.,
which shortens the fix and wash time (most papers fix in about
30 seconds) since it limits the amount of fixer residue in
fiber based papers. Hypo clear, and then wash in an archival
washer for 20 minutes.

The best way to tell if you are washing properly is conduct an
HT-2 fixer residue test. Do a search in rec.photo.darkroom for
washing, HT-2, etc. and there are lots of thread and formulas
on this.

Course RC papers always require much shorter wash times...

  Using a wash aid such as Kodak Hypo Clearing Agent will
very substantially reduce wash time and the amount of water
used. Wash aid used on film reduces wash time by a factor of
about 1/6th, with fiber paper about 1/3rd. RC paper washes
out very fast and doesn't need wash aid.
  Some running water washers used considerably less water
than others to do an effective job. The water at the surface
of the film or paper is where the washing is done so a
rapidly changing thin film of water is sufficient. High
volume, so called archival, washers are water wasters.
  You can wash in successive changes of water. The number
of changes depends on the overall wash time needed. Wash
time remains constant for both running water and successive
change washing.
  Kodak and Ilford have insructions for washing in
successive changes of water. The Kodak method uses constant
interval, the Ilford method uses increasing intervals. They
are equally effective but the Ilford method probably uses
less water. The reason for using increasing intervals as
washing progresses is that washing is a diffusion process
which varies in speed with the ratio of the concentration of
hypo in the emulsion to that in the wash water. The hypo
comes out very quickly at the beginning of washing and much
more slowly as washing progresses. It is essentially an
inverse square law function.
 Since film will wash out in about five minutes when
treated with KHCA two changes of water of 2-1/2 minutes
each, with constant agitation, is probably enough.
  BTW, your well water may be either hard of soft. Hard
water is more effective than soft water for washing. The
most effective of all is sea water. Kodak wash aid is the
result of research into why sea water is so effective. It is
actually more effective than sea water.