RTLs have 1 1/2" - 2" ports, depending on the size of the filter.As far as installation though, do they just go inline of the pump and hardplumbed in?
This is the picture the guy who sold us the RTL-25s gave us of a setup he did.
This is our setup for our 300 gallon tank:
There is a free standing base that can be purchased for RTLs. The RTL-100s for our big setup will be sitting on the floor.
All Aquatics sells RTLs, so I'm not the only fishkeeper using spa filters.
http://all-aquatics.com/store/item/...RTL_100_Dynamic_Series_Commercial_Filter.html
There are a few other elements in my picture. There's a line from a 55 gallon holding tank. (We open the valve, and water gravity flows into the main tank through the filtration plumbing) Not in the picture is a utility sink with a connector to the holding tank. We just turn the hot/cold water on to keep filling the 55 gallon tank that feeds the main tank. On the extreme right is a line going down under the house and out on the patio. When we open the valve outside, water starts draining out of the main tank. Super easy water changes