Yes, this filter is used for the vacuum suction function. You do not need to replace it after every use, but please replace it promptly if the filter becomes dirty, damp, clogged, or loses suction power. Regarding the EMS patches, if the patch is still sticky, conductive gel is generally not required. Please apply it to clean, dry skin. If the patch has dried out or is not making good contact, you may use a small amount of water-based conductive gel. Please avoid using oil-based products.