The plunger on my manual Groco HF seems to be shot - it just goes up and down without resistance and without pumping anything. I figured I would replace the head with the manual JABSCO 'twist & lock'. It appears to be the same - same size and same connection sizes.
I was hoping you guys could tell me if that is doable.
It's do-able...but for very little more $$, you can upgrade to the toilet that's been rated #1 for decades--the Raritan PH II or PHC (compact version that uses the same pump)...check it out here:
sbo.com PHII PHC LBA A bunch of people here have gone with that toilet and every one of 'em only wish they'd done it sooner.
I was also hoping you could tell me what I'm in for here. I'm pretty handy with tools but I'm not a plumber. Will seawater flow in when I disconnect the old head? I have a separate bilge pump and float switch right there for the shower..
It will if you don't close the inlet seacock first! In fact, if you don't do that every time you leave the boat, you're just asking to sink your boat...
If you do decide to upgrade your toilet, you'll have to drill one or two new mounting bolt holes...that's not a big deal. And btw, toilets mount using lag bolts, so there are no nuts on the bolts.
As for the rest...Your new toilet will come with installation instructions...I strongly recommend you read 'em and ask any questions they don't answer BEFORE you start this project....'cuz it's always cheaper and easier to do it right the first time than it is to do it over. Pay special attention to the instructions for installing a vented loop (anti-siphon device) in the intake. All toilets installed below the waterline are supposed to have one.
It's just occurred to me too...that if your toilet maintenance has been neglected for so long that the piston seals and o-rings are so worn they can no longer pump at all, it's unlikely that the rest of your system--hoses, hose connections, clamps, tank, y-valves etc--has seen any maintenance either. So I suggest you also spend a little time reading threads in the Headmistress forum...a lot of good information there. The link in my signature will take you to a comprehensive "marine toilets and holding tanks 101" manual that will help you learn to operate and maintain your system to prevent problems instead of fixing 'em.