Backflow in Head

[Howler]

On our new-to-us sailboat, we have an interesting head problem.

SYMPTOM - There is backflow into the bowl, even after flushing for a long time to clear the sewage hose. The water flowing back is clean, but contains organic particles.

SETUP - Dometic MasterFlush 8700

DIAGNOSIS -
- I've disassembled the macerator pump and it's clean and functional.
- I checked the duckbill joker valve and it's like new.
- I checked for blockage in the air vent to/from the holding tank. It's clear.
- I even replaced the sewage hose, thinking there might be blockage. There was no blockage.

There is a 12 ft. run of sewage hose bewteen the head and the holding tank that includes a 7 ft. vertical rise. This is probably causing a lot of the back pressure and making it difficult to lift the solid components of the waste to the top of the holding tank. There's nothing to do about that without re-architecting the boat.

Any other suggestions (Peg, please chime in... nothing in your book I could find about this)?

Thanks!

[leecea]

We get backfill and replacing the joker valve usually cures it for a while. I just put a new one in. The one I removed looked fine. But no more backfill.

We have a similar long run etc to the holding tank and perhaps the joker valves need to be in 100% condition to resist the pressure?

I don't know but I do need to change them once or twice per season and our head use is pretty light because we are in a marina a lot and use the land based facilities when we can.

[Tin Tin]

Our old cat had Jabsco quiet flush heads and they did not just rely on the joker valve on the head unit, they had a second in line Whale check valve between the head and the higher holding tank. This worked ok, but when it came time to renew the check valve it could get ugly. We now have fresh flush and a 180Lph water maker and I have to say that it is bliss in comparison in terms of maintenance and odor.

[Tsuru]

I'm in agreement with Leecea above. I change our Joker valve at the beginning of the season. For any reason if I open and inspect the Joker I'd replace it. Mine all look fine but will backfill when they get old.

We have a loop with syphon breaker on the outlet of our head. Not 7' but pretty high. The run to the holding tank is about the same.

#1 Ensure the vent is clear. I know you have already checked but take the pump out cap off. Check to see if you have a carbon filter in the vent line. If so, I'd remove it (IMHO).

#2 Change the Joker valve. Even bad ones look good. Keep some spares and change regularly.

Let's see what the experts come up with.

[peghall]

My first thought was a blocked tank vent (which still may be a possibility) until I saw that your toilet discharge line is about 12' long and includes a 7' rise. There's no way for bowl contents to make it into the tank without a lot of help from graviity and 4' is about the max that any marine toilet can lift bowl contents. There is a solution that shouldn't require "re-architecturing the boat" but does require re-routing the toilet discharge plumbing to provide that help from gravity. But first some questions, starting with: 1. Why is the top of your tank 7' above the toilet discharge fitting? 2. Can the tank be lowered at all without any "re-architecting?"


It'll be easier for me to help you solve this problem if we can move the conversation to email to work out the details of what can and can't be done....I'll post the solution here. If you'll send me a PM I'll reply with my email address.



--Peggie