Hello! I am new here and would love some help. I have a check valve on my main sewer line that’s attached to a reservoir with a sump pump. The flap for the check valve seems like it’s way too heavy and whenever there is a simple toilet flush, the toilet paper doesn’t make its way through the valve. There has to be a huge rush of water like from the washing machine or a full bathtub and then I see the flap open a little bit. Not even fully. I thought of taking off the cap to clean it and make sure there is no grime or sludge on it but it seems to be locked with a screw that’s secured by a nut and the ac res itself is bent outwards at the end so I can’t simply twist the nut off. Any thoughts or ideas here? Is this how they are supposed to work? How do I get the flap off for cleaning?