Once the smell permeates surfaces outside the tank, it's not easily rid. Our boat had probably 10 years of toilet abuse, and was left with the contents inside the tank with a plugged vent for the 2 years that it sat on the hard before we purchased. After replacing all upholstery immediately, I tried cleaning surfaces for 2 years with not very much success ... granted, I have a sensitive nose. I bought Peggy's book and followed all advise. Finally, after pulling the head out and leaving it in the driveway for a few days, you could smell odor from 10' so you can't tell me that the toilet won't smell even if it is cleaned properly. It was a virtually gleaming, brand new-looking head when I removed it, even though it was original to the boat, but it smelled incredibly bad. But it is true that the hoses were the worst offenders. It was not an easy job to replace the hoses, epecially during the summer months and I never want to have to go thru this exercise again!
Besides that, nobody has ever done #2 in our boat in 8 years and because all our sailing is day sailing we pee while on the boat very infrequently. I flush the tank often with fresh water from the lake repeatedly and pump out often just to try to eliminate all trace of odor. The interior of the tank still stinks to high heaven even though it is vented properly and hasn't had anything but fresh water in it (pumped out frequently) for the past 6 years and the exterior of the plastic tank also has an odor. The odor WILL saturate the tank walls to the exterior and I believe it is virtually impossible to eliminate once that happens. Even the fiberglass has odor, but much of it is too remote for me to reach while cleaning, not that the cleaning really eliminates the odor once it permeates the material.
I also agree that bilge odor is also difficult to deal with. With enough water dripping from the packing gland, and rainwater entering from the mast, it was virtually impossible to dry out the bilge. Finally, with PSS system, we no longer have water leaking at the shaft, but I can't do anything about the rainforest conditions that we have in New Jersey. I swear, the Pacific Northwest is a desert compared to our climate. The PO was not clean about oil and diesel either and it was a battle to clean the bilge to the point where an oil slick doesn't form while pumping bilge water. It is really difficult to get to all the nooks and crannys while cleaning the bilge and the unfinished edges of fiberglass construction is hell on your hands and fingers!
These are the significant things that I will be looking at when looking for my next boat, believe me!