My Plumbing offices & workshop is situated right beside a pump station, sometimes, if the pumps fail, then the sewerage backs up my house drainage blocking off the vent line & therefore bubbles the pan, I removed the old pan & installed a vented pan & vented it through the roof. We also have a problem with green tree frogs, they crawl up the drainage & eat the septic flies then crawl into a warm spot, usually a vent, this sometimes blocks up a vent & renders the vent useless. again bubbling in the pan happens when the pump station fails. Common sense tells me to poison the frogs, but I am a softy. inversion, siphonage, frogs. I think I’m going mad. Is it a conspiracy?.