With regards to the tank vent filter, we are planning to use Peggies suggestion to just remove the filter and install a new line for more efficient air movement. Plus, I think she’s spot on about flushing the line occasionally. I know we probably plugged the filter with too much stuff in the tank and rolling a bit at sea. Filters cost from $75 to $150 and I’m beginning to think they are a scam. And Tom on ASD makes his own out of PVC and bulk charcoal.
With regards to the gauge not working. On the top of your black waste tank are two Removable panels. The one with wires coming out of it are your level sensor’s. We just unscrew the big plastic ring every year or so, and remove the sensors and housing as one unit. Then plug the hole with a old towel (it helps if you do this right after a pump out or discrage). Set The Whole assemble in a bucket and let it soak in a 50/50 solution of vinegar and water for a few hours. Sometimes I have to use an old toothbrush to assist in removing “stuff”. Before you reinstall the assembly back in the tank, move the sensors up and down the plastic bar and watch the tank gauge to make sure it works right. Ours has 3 floats, and the bottom one is for first light and the top one is for the red light. I do remove a few of the cable ties so that the wiring doesn’t get all twisted up while removing and reinstalling the assemble into the tank. By the way, we have an FRP tank. Pretty sure all the Selene’s are FRP but dont quote me on that one.
Best of luck!