More about avoiding plugs than head
When I first started cruising I experienced several plugged heads, a couple of which required head diassembly. (not my favorite boat maintenance
chore.) Disassembly or not, the problem has always been something (hopefully t.p.) stuck under the discharge flapper valve so it doesn't close and make a seal.
It occured to me the problem might be from the fact that most people are used to flushing
everything at once which greatly reduces the possibility of a plug
. What I now tell visitors is to start pumping right away, so nothing gathers up in the bowl. I tell them to go ahead and use t.p., but to also continually pump this through. Since instigating this practice, I've never had to deal with a plugged head either on my boat or any of the charter
boats I've been on. In addition to less moving through the system at one time, this has the advantage that if any t.p. does get stuck somewhere, at least all other waste has already been pumped through. The pumping noise
also covers up another other noises one might not want others to hear.
I'm sure the quality of the head also matters, but I've found the above to be very helpful.