Haven't had a chance to do additional load testing for the Grendel because of a crappy situation.
The Boss took a bath and it wouldn't drain all the way, and the toilet was bubbling. The pump up toilet in the basement pumped up into the bath tub and overflowed the toilet in the main level. One hell of a shitty mess. A day later plumbers ran a camera down the vent and managed to push the clog down stream. The camera showed a partially collapsed pipe with some roots that was collecting solids. So for a few days we didn't put any toilet paper into the system.
Yesterday plumbers started digging up the pipe that runs to the septic tank. It leaves the house under the concrete patio and runs under the concrete, parallel to the house, for about 60 feet. The sewer pipe is a thin wall polymer of some kind. About 12 feet were at least partially collapsed. The collapsed length has now been temporally replaced with schedule 40 PVC. All joints are fitted but not glued because I'm having the total length sleeved internally, old and new, to strengthen and prevent future issues like this.
The sleeving may be a week away, but the system is useable again.
Thankfully our fifth wheel camper sits next to the house, so at least we didn't have to rent a porta potty.