sewage injection pump seal

I have a Water Ace sewer injection pump for pumping waste from my washing machine and utility sink in my basement. It is an above ground unit housed in a plastic bin. On the top there is a small access hatch to pull/clean the filter. When there is high pressure water coming in (from the washing machine) a very small amount of water seeps out (about the size of a quarter puddle on top). It's done this since I just cleaned out the filter. I just moved in and this is the first time I've had to clean the filter. Is there something I should use to create a better seal next time? Remember it has to allow me to remove the cover to clean again in a month or two. Thanks for advice!!
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file
Upload is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.