I have two Lavacs, one in the forward head and one in the aft. Due to differences in layout, one was plumbed somewhat differently than the other. The forward head worked easily, did not get the seat wet, rinsed the bowl clean. The aft head pumped harder, soaked the lid and seat, and often did not leave the bowl clean. After some experimentation, "Head - to - Head testing" as it were, the aft head pump was relocated lower (made a little difference in pumping effort), the vented loop was lowered and shortened (also helped pumping effort and rinsing), and the pump was changed from 3 o'clock/9 o'clock orientation to 6 o'clock/high noon orientation. This latter detail is rather explicit in the instructions, but inconvenient in the first instance to accomplish in the aft head. However not doing so make the one way valves in the pump very inefficient and slow to close, so that on each stroke of the pump there is a significant backwash before the valve seals - that is what results in a geyser from the bowl outlet and a wet lid and seat. The size of the vent hole in the vented loop has to be tuned to the installation so that the vacuum created by the pump will leak down in the desired time. Once all this was figured out and corrected, the aft head works nearly as well as the forward one.

So while they are picky about installation, once you get it right, there is very little to go wrong in the head. No metal parts are exposed to effluent. There are no sliding or rotating seals anywhere. The pump is dead simple, and easy to access without tools to unclog if it is every necessary. The gasketed seat and lid might be the theoretical weak point, but in practice seem to cause few problems.

One more tip for installers: anything that does not get beyond the pump outlet valve, or perhaps even beyond the exit vented loop, will eventually leak back to the bowl: no one way valve of this type is perfect. So in planning the plumbing, consider the volume of hose involved, and shorten it as much as possible, if necessary add a trap to insure that the bowl is not too full after all has settled. Two things control how much water is left in the bowl after a flush: the time it takes for the vacuum to leak and the inlet hose volume, and the exit hose volume that can leak back to the bowl.