What you're trying to do won't work. Instead you need to CONVERT your manual toilets to electric
toilets...and to do that, you don't keep the manual pumps...instead you have to buy the conversion kits ( everything except the bowl, seat and lid)--one for each toilet. They can both use the same intake thru-hull.
Check 'em out here: Conversion Kits > ITT Flow Control - Engineered for life.
Click on each one to to see what's involved...click on Downloads to get the installation
Avoid the 29200...it looks to be the simplest--and it is. But it also draws almost twice the amperage, makes enough noise
to wake the dead and costs more than most complete electric
While you're checking out conversions, take a look at the Raritan
SeaEra...also available as both a complete toilet and a "conversion." Much higher quality, exceptionally reliable/durable. In fact Practical Sailor just rated it the "best budget" electric macerating toilet. You can read all about that one here: Raritan Sea Era