I send through a patch with solvent and wait 5 min.Then Idip my brush in the solvent and sent that through4-6 times. Then I sent through a dry patch and repeat this process until the patches are not discolored. I recently bought a gun that was very fouled. I had to take Hoppes Benchrest and let it sit overnightas it had alot of copper build up.She's now clean but it took some doing.