Dunn Edwards Paints and Home Depot has white plastic buckets for under $5, HD has white lids for under $2. The lid you're looking for have a black rubber gasket deep inside the grove. The lower strip will peel off exposing about 12 tabs, pop the tabs one at a time to pry open. Paint stores should have a tool to help remove the lids. You can push lid on by hand if you put your weight into it, 2 x 4 works well (don't be afraid to give it a good whack).

The Plumbing Department has PVC screw apart connectors, if you place them on both your inlet and outlet lines going to the lid it will make for easy removal. I would leave the lid on and just dump and rinse though these openings.

Another product that I use a lot of is "Plumbing Goop" by Amazing it come in a purple 3.7 fl oz squeeze tube. Let it cure for about 48 hours of until it no longer smells before placing it in water.