In electronics work, it's handy to make up a probe which contains a resistance of a few hundreds ohms and a lead terminated with a crocodile clip. You can clip to chassis and then use the probe to make sure filter caps are discharged before working on them.
The "regained" charge phenomena is quite well known. In HV power supplies it's fairly common practice to make sure the caps are discharged as described and then use a straight clip-to-clip lead to short them out.
