I have a 2015 338RETS. Don't know if they changed them 2017. Mine are all outside. The cold and hot water drains are side by side. They are under the trailer between the two slide outs near the grey tank dump valve. These two pull up to drain. The other two are for the fresh water tanks. One near the previous valves and the other one is under the big slide out. These two have a little handle on top. Hope this helps.
2015 Jayco Eagle 338RETS
2004.5 Dodge Ram 2500, Quad Cab, 4X4, CTD