Head

Fair enough!

So, with your anticipated use, and assuming you DON'T have a separate holding tank... I'd probably cap off the ports on the back of the potti, plug the lines and just use it as a regular portapotti. This would make the system dirt simple.

The potti has two securing rings screwed to the floor - and there are quick release clips on the side. Then, the top half (holds water) cleanly/easily disconnects from the bottom half (holding tank). Then just take the bottom half to a toilet and dump it.

Or... maybe it would just be easier to buy a new potti (no ports on the back for hoses). They're very inexpensive - FYI. a potti with hoses will be labelled "MSD".

But, look into what you have and check the boat for parts. You should be able to cap that one off
 
I have a working head with holding tank on my 268 Islander. It's almost never used as a head. I line the toilet with the black 5-gallon bags that the bucket head uses and have a small disposal bucket next to the head. Primarly used for #2 by the boys.

It is a little inconvenient but less troublesome.