Occasionally, it can be difficult to find a way simply to introduce a purging compound into the production system. Especially in large equipment, the feed system may be fully closed from the supply silo to the throat.
If this is your situation, look for an auxiliary feeder port or a hopper magnet drawer that can be removed to allow access. If a substantial amount of purging compound must be fed into the extruder it may be possible to fabricate a chute or funnel from sheet metal or even cardboard and rig it to a temporary access opening. A little mechanical creativity will usually save the day.