From AIM 6-3-5:
a. Should it become necessary to dump fuel, the pilot should immediately advise ATC. Upon receipt of information that an aircraft will dump fuel, ATC will broadcast or cause to be broadcast immediately and every 3 minutes thereafter the following on appropriate ATC and FSS radio frequencies:
EXAMPLE-
Attention all aircraft-fuel dumping in progress over-(location) at (altitude) by (type aircraft) (flight direction).
b. Upon receipt of such a broadcast, pilots of aircraft affected, which are not on IFR flight plans or special VFR clearances, should clear the area specified in the advisory. Aircraft on IFR flight plans or special VFR clearances will be provided specific separation by ATC. At the termination of the fuel dumping operation, pilots should advise ATC. Upon receipt of such information, ATC will issue, on the appropriate frequencies, the following:
EXAMPLE-
ATTENTION ALL AIRCRAFT-FUEL DUMPING BY-(type aircraft)-TERMINATED.
No minimum altitude specified, but fuel released into the atmosphere will vaporize quickly. To "wet" a home with JP, IMO you'd have to be about 2000 AGL or so with the dump rate of the average aircraft. More often than not, you'd be far higher than that.