Before doing ANYthing, read...
There are several articles in the Head Mistress forum Reference Library that address various sources of odor, how to test for them, and the cures. It may be your hoses--but find out before replacing them. It may have nothing to do with your sanitation system...we get calls all the time from people who've replaced their entire sanitation system without getting rid of odors, when all they really needed to do was clean their bilge and/or sumps. So the first step is: find out what's causing your odor. THEN fix that, instead of blindly trying everything. But answer your question about the vented loop: it's one possible source. There should be a check valve in the nipple at the top of the loop that only lets air IN, not out...but if the check valve is missing or has failed and needs to be replaced, it can allow odor to escape. However, if odor is escaping, so should anything else that goes through it...it would also squirt something when the head is flushed. If it's not doing that, then I doubt that the vented loop is the culprit. You'll find a LOT of good information in the articles...and after you've read 'em all, if you still can't find the source of your problem, I'll be glad to help.
