I am late to this thread, but it sounds like the water pump is cycling and you suspect the head. Then you have ordered duck bill valves, as well as some parts for the head? Our vacuflush needed attention when we purchased our 2000 380DA. There was a vacuum leak that caused the vacuum pump to keep cycling every 10 minutes or so. On a quiet night you could hear the vacuum leak 'hissing' in the head. I purchased a gasket kit, got an old shirt and some rubber gloves, and replaced the gaskets. No more vacuum leak, and everything was happiness. Then someone flushed something and stuck a duck-bill valve. Same symptom(vacuum pump cycling about every 5-10 minutes, 'hissing' sound back by the holding tank this time) I purchased new duck bills, but one of the club forums here suggested filling the toilet bowl with water/ treatment(in my case we use Odorlos) then blasting a big wad of water through the system with a single flush. This has worked for us twice now. I still have the duckbills, new and ready to go if needed. If the WATER PUMP is actually cycling, you should find where the water is going. In rare cases the pump itself can lose pressure, but usually a cycling pump means a water leak. If it is leaking at the head/foot pump there should be water under the head. I do not think it can leak into the vacuum section, but if it did the vacuum pump would also cycle. The holding tank is after the vacuum section, so a crack (or leak) in the main tank will not cause either the water pressure pump, or the vacuum pump to cycle(it can however make a horrible mess that is hard to clean up). When we had a small mystery water leak, causing the water pressure pump to cycle every hour or two, it turned out to be the water heater. I did not find it until it really broke loose on a trip to Monterey.
I do not think 30 seconds is too long. The 380DA has the head forward of the kitchen, by the V-Berth (So we have a longer pull to the holding tank than a 340DA) but our vacuum pump runs about 30 seconds after each flush. However, we can be away from the boat for a few days and when we turn the switches back on there is still vacuum, and water pressure and neither pump runs until we turn on a faucet or flush the head. Your vacuum pump run time should decrease a little when you fix the leaky gaskets in the head. If you have moisture and rust under the water heater, I say fix it now. Do not wait until the middle of your vacation. There is a Confucius saying something like "a journey of a thousand miles begins with a leaky toilet valve, and a broken steering gear"(or blown water heater?). Ideally, when done at your home port, we refer to these type of repairs as "yachting", if you have to do them in some exotic location during a vacation that is "cruising". I console myself with how much money I could spend and still not make up the difference in sales tax on a new boat (which would still have issues), and that no matter how much I spend to repair existing systems, I still just pay taxes on the purchase price of a used boat. When I am gorping through the bilge, or repairing the head, I remind myself of this quite often:grin: Over time, having struggled through these repairs, you will gain a much better familiarity with your boat, and become less dependent on Marine "professional's".
