Stupid question but am I harming anything if I close the inlet seacock to the toilet but leave the outlet open, then flush the toilet with freshwater from the shower or a container?
I did this for years before changing boat. Couldn't stand the smell of rotten seawater each time I visited the boat. I would still operate the seacock each time I visit though to keep it free and operable.
Just pour fresh water down regardless and leave both open just in case you need to use lots of water!!
I have rigged up a shower hose that I hold onto tap and let the domestic pump fill bowl. That way the domestic doesn't actually connect to waste and risk any backflow!!!
When not used it hangs up in shower cubicle.
The last 2 winters on hard standing i have filled inlet pipe with Milton for 5 weeks to sterilise the pipe and this has made a huge difference. I discharge the Milton before relaunch !
It's not just me then! The stench of rotten eggs each time we use the heads is overpowering yet it has been cleaned out recently. I will connect to fresh water for sure.