You will need a holding tank...
It may not have to be a very big one unless you plan to spend a lot of time in the Keys, 'cuz the discharge of treated waste is legal in at least 90% of the waters you plan to cruise except for the Keys...they're all NDZ...you'll have to use a tank while you're there...and btw, in the Keys, the "3 mile limit" is
TWELVE miles on the Gulf side, but still 3 miles in the Atlantic.
If you don't have a manual for the Lectra/San you can download and print one (and I recommend that you do print it out and keep it on the boat) from the Raritan site:
Raritan Lectra_San MC manual Maintaining it isn't hard, but it is VERY important...so learn what the blinking lights mean and what to do. In warm waters, it can necessary to clean the electrodes as often as every 3 months or so.
As you've prob'ly already learned if you've spent any time in this forum, your best source for a tank is Ronco Plastics
Ronco Plastics Marine Catalog
You'll want a gauge for it...this one:
Profile Tank Monitors
And while you're on the Raritan site, I suggest you check out the "hold 'n' treat" controls--not the whole package, JUST the controls, which can be retrofitted to any existing Lectra/San, PuraSan or ElectroScan and tank.
http://www.raritaneng.com/products/waste_treatment/holdntreat.html
Give me another shout if you have more questions...meanwhile have a good Thanksgiving!