Thank you for contacting RIDGID.
At this time, we do not make a wet filter available for WD4070, only the VF3500 is the filter that can be used on the said model.
When picking up small amounts of liquid the filter should be left in place. However, when picking up large amounts of liquid we recommend that the filter be removed. If the filter is not removed, it will become saturated and misting may come out of the exhaust.
Also note, that when picking up large volumes of liquids, the liquid in the drum may reach a predetermined level and the float mechanism will rise automatically to cut off airflow. This occurs to avoid liquids from entering the power head. When this happens, turn off the vac, unplug the power cord, and empty the drum.
If you do leave the filter in place while picking up liquids, the filter must be dried to avoid possible mildew and damage to the filter. We recommend that you clean the filter and then let the filter air dry overnight. Make sure that after each cleaning, you check the filter for holes or tears. You will need to replace your filter if it has any damage.
Please remember to never leave your wet / dry vac unattended when it is turned on and to always uses your wet / dry vac in accordance with the owner’s manual.
Lastly, refer to the owner’s manual sent on your email concerning the proper usage of your vac.
If you have any further questions or concerns, feel free to call us at 1-800-4-RIDGID (1-800-474-3443) or you may send your email to [email protected]