The actual process of getting a detainer lifted is not all that difficult. However, convincing a judge to actually lift a detainer is a completely different subject. For example, an attorney can file a motion for a hearing with the prothonotary in the appropriate county and ask for a date before the judge. That is very easy to do.
On the day of the listing, the lawyer will appear along with the defendant, a lawyer from the DAs office, the probation officer and the judge. The defense attorney then must convince the judge as to why the detainer should get lifted. Some judges are very very difficult about detainers. The real issue becomes whether there have been any issues with the probationer while they were on probation and what are the circumstances of the new arrest.