Smelly Head

[tanksalot]

Our head (Ericson 27) is piped directly to the top of the holding tank, without a "loop". With a half-full holding tank on a port tack, the liquid is near the top of the toilet. There's also a chronic smell that we can diminish by cleaning but never eliminate. I'm thinking of putting in a vented loop to prevent backflow, but am concerned about the amount of flush water needed to clear out the upward leg of the loop. (Thus the holding tank would fill up sooner). Are MOST heads plumbed with a vented loop and we've been putting up with the smell unnecessarily? Is my concern of excess liquid in the holding tank valid?
Thanks in advance!

[osirissail]

You should not be getting back flow from the holding tank to the MSD (toilet). In a hand pumped MSD there is a "joker" rubber valve on the outlet of the MSD. This prevent back flow into the bowl of the MSD. This "joker" valve can "lime up" with scale and then it does not close allowing holding tank liquid to flow back into the bowl. Check that first.