Thanks for the question. You can backwash this by shaking it! As for checking the filter, MSR recommends doing the following steps to check it's functionality:
1. Hold the filter at about 45° and prime it by squeezing the Bulb (G)10 times. 2. Pump 3/4 liter of water into a bowl or pot.
3. Unsnap the Prefilter (M) from the Female Check Valve Housing (L) (put it in a safe spot).
4. Unscrew the Female Check Valve Housing from the Male Check Valve Housing (J).
5. Remove the Check Valve (K) and reverse its direction. Place it back into the Female Check Valve Housing.
6. Screw the Female Check Valve Housing back onto the Male Check Valve Housing.
7. Remove the Spout (B) and Umbrella Valve (C).
8. Place the Cap (D) into the bowl/pot of clean water and pump 1/2 liter of clean water backward through filter.
9. While the Cap is still submerged, squeeze and hold the Bulb. Then remove the Cap from the water and release the Bulb.
10. If Bulb re-inflates within 30 seconds, the filter is NOT SAFE. (NOTE: If a few bubbles escape the Check Valve, unscrew the Female Check Valve Housing, reseat the Check Valve, and screw the Female Check Valve Housing back onto the Male.) Then test the filter again.
11. If Bulb stays compressed, the filter is safe to use.
Date published: 2018-02-11