"Can I safely use an air admittance valve (or "auto vent") on any of the above systems?"
Although some people have installed an air admittance valve on the above systems, we will never suggest or recommend that you do so. We always recommend installing a vent all the way to the roof (and as per your local codes). We have had people write us stating that when they installed an air admittance valve the flapper in the valve can chatter and create vibration. The right way to go is to install a non-mechanical vent, all the way to the roof, and as per your local codes.
"Can I cut off the plug from the end of the Little Giant RS-5LL remote switch that's used on the smaller Drainosaurs so that I can hardwire it into my system?"
No; not only would that void the manufacturer's warranty, removal of the plug from the RS-5LL switch (which is used on the WRS-5, WRS-6 and WRS-C6 systems) will not allow the switch to function properly (if at all). Pressure from rising water pushes against a diaphragm inside the RS-5LL switch, turning off the switch. For the diaphragm to move, the air above the membrane must be expelled; to allow this air to escape, a small vent tube runs from the top of the switch and along the cord, exiting at the plug. If the plug is removed and the switch is hardwired, the air tube would essentially be "plugged off"; the air from the area above the diaphragm membrane could not vent, which means water pressure would be unable to move the membrane to close the switch.
We hope that we have helped you with drain systems at PlumbingStore.com