Toilet and grey waste holding tank solutions?

[SlowlyButSurely]

+1 for Tek Tanks. If you follow their design you will end up with an installation that does not smell.

 

[ashtead]

Just remember once you start installing tanks the risks of blockage increases due to pipe run. Retro fitting in a westerly seems like a considerable expense but have you thought of looking at boats of same type for sale to see what possible solutions exist. Personally if med sailing is desired might be tempted to buy a nice Moody local with tank already installed ?