In addition to the Fed EPA laws I listed above, local laws may apply in marinas (but nowhere else).
In my part of CA local law prohibits use of a Type 1 system in a marina where a restroom is available. We have nice restrooms at the marina, so I have no need to use the Purasan at the slip. You can always have a Y-valve set-up that routes your head from the Type 1 to a tank system and use the tank at the marina like you did before.
If you can use a Type 1 system legally in a marina and have a below the waterline thu-hull for discharge no one will be able to see or smell the Type 1 flushing.
That's not the case when I notice illegal discharges from non-Type 1 tank systems at the marinas, which I have witnessed on numerous occasions at several locations. That's a filthy practice that looks as bad as it smells.
You can download the complete owners manuals for the Purasan and Electroscan systems here. Those will have every detail you could possibly need. I bought my Purasan from BoatFix several years ago.
http://www.raritaneng.com/products/waste_treatment/index.html
Here is how the Purasan works. When you flush the head some of the fresh flush water (not water in the bowl) runs up a vinyl tube to the disinfectant tablet dispenser. This water mixes with the tablets at a metered rate and runs back down into the Purasan treatment unit.
The treatment unit (the main blue box) has two chambers. The disinfectant is added to the waste in the first chamber and macerated. The next time you flush that treated waste moves into the second chamber where it gets mixed again. The third time you flush that treated waste gets pushed out of the second chamber, through the discharge hose, the vented loop and finally out of the thru-hull.
So, every time you flush, the Purasan moves new untreated waste into the system and pushes treated waste out through the thru-hull.
The actual treated waste discharge looks like cloudy water which disappears about as soon as it leaves the boat. I have a below the waterline discharge thru-hull and have never actually seen the discharge in four years of use. I've looked, but I never have seen or smelled anything.
Several of my friends have Lectra-San, which is the first version of the current Electro Scan. It looks a lot like the Purasan but it's a completely different unit that uses salt water and electrodes to disinfect the waste. The rest of the way Electro Scan operates is pretty much the same as Purasan.