Steven,
I have two rent house pools with DE filters, so when I built a pool at my house, I wanted a DE filter. Almost all the cities in the DFW area require that DE filter be plumbed to the sewer, not the street or storm drains.. Of course the sewer is on the front side of my house and the pool is in the back, so we opted to go with the CCP-520 cartridge filter. At the time, I was very disappointed.. But, after using a cartridge filter for the past 5 or 6 years, I find that I like the cartridge filter a lot more that my DE filters. I cannot tell the difference in water quality at all. I now can hardly wait for the rent house DE filters to die so that they can be replaced with large cartridge filters..
That said, we do not swim at night and the DE filters that I do have are not the quad 100. I do know for sure that getting rid of the multiport valve is the only way to go. I no longer backwash my DE filters because all the pools have IntelliFlo VS pumps that run at low RPMs.. This keeps the filter pressure low and allows me to only need to open and clean them twice a year. I do the same for my cartridge filter, even though I could go a whole year between cleanings, if I wanted.
For sure I would check with your city about the backwash to the sewer requirement..
Thanks,
Jim R.