Step 1. Unless the boat already has one, have your boat hauled to install a 3/4" intake thru-hull and seacock below the waterline. It should be conveniently located next to the head so that there is no excuse not to keep the seacock closed except the when the head is actually in use. Step 2. Measure the space in your head BEFORE selecting a toilet. Make sure that wherever you have to mount it offers adequate clearance for both the front and the back of the bowl, room in front of the bowl for your knees when you sit on it, and enough side to side room for the pump. Step 3. To gain ANY advantage over a pumpable 5-6 gallon portapotty, you'll need an 18-20 gallon tank.Find a location for it that's within 6-8' of the toilet that will give you a relatively straight run from the toilet to the tank. The further forward on a sailboat, the better (Read "Odor--Cause and Cure" in the reference library of the Head Mistress forum before spec'ing out the tank installation). Step 4. Drill two more holes in your boat above the waterline--one in the hull for the tank vent, the other in the side deck for the pumpout fitting. Step 5. Measure your hose lengths...add at least 2 more feet to each section than you think you'll need. Be sure to allow for a vented loop in the intake line that's at least a foot above the waterline at any angle of heel. Step 6 Read the article that explains how to put hoses on fittings. Step 7. Go shopping for a tank, hoses, fittings, enough hose clamps to double clamp all connections, a pumpout deck fitting, a thru-hull fitting for the tank vent, a vented loop, and a toilet and bedding compound. (Be prepared to spend at least $500) Step 8. Recruit help that's knowledgable and experienced when it comes to putting holes in your boat. Step 9. Set aside an entire weekend--after you've installed the intake fitting and seacock--to do the job.