I was thinking the same thing. I have a 24ft pool. I have the cartridge filter, and I just purchased the sand filter. I have the two inlets that come to the T connection, and I just purchased the single fittings. I was thinking of running them both at the same time (not all the time, but for many hours at once) when running lets say the automatic vacuum.. I figure run the sand filter with the auto vacuum and skimmer, and then the cartridge to continue to clean up the water or vice versa.. Or when vacuuming. I mean, I am trying to understand from reading through this thread, since those tubes are smaller on the inlets, will restricting to one inlet on each cause any damage to the pumps? The sand filter is rated to 3000gph, and I think the cartridge is 2500gph.