It's in the user manual I have but seems to be overlooked a lot. Maybe that is a good thing as the parts list is/was incorrect for that year (just for a change!). I took mine out and could not get it to seal again. GF managed to get the correct washer in time cos they had the same problem. I managed to seal it with an oversized copper washer and a green o ring used for automotive a/c pipes set inside the washer. Works better than the original so far. I think the filter there instead of the flat sump strainer that is under the sump plate on the earlier models but I am not sure.