In my subscriber-exclusive series on central vacuum trouble-shooting I mention the importance of keeping the screen at the central vacuum clean. Casual observation is not normally adequate to check the screen, however.
The screens are usually in a transparent plastic housing. What most people don’t realize, however, is that fluids flow through the screen from the inside out. This means, a glance at the screen through the bowl will not allow you to see any debris that has accumulated. You need to remove the canister and look inside to properly inspect the screen.
If there is debris, you can usually just clean the trap out, but disposables are available as well which can be a more tidy solution. If the screen is upstream of your amalgam separator, spent screens or any waste within it must be treated as amalgam scrap and be properly disposed of accordingly. If downstream of your separator, it is generally just regular unregulated waste (regulations will vary by location, however, so check with your local authorities if uncertain as it may qualify as biohazardous or need other special handling).